Current sensor

Abstract

A connection arrangement for a printed circuit board, PCB, implemented current sensor is provided. Vias at an outer circumference of the measurement coil are positioned at different radial distances, allowing the start and end of the measurement coils to be positioned closer to one another. The coupling of the coils to a circuit is provided using connection conductors provided on a first layer and a second layer, with the connection conductor substantially aligned in the same plane.

Description

[0001] CURRENT SENSOR

[0002] Technical Field

[0003] The present disclosure relates to connection or hookup arrangements for current sensors, and in particular to connection or hookup arrangements for printed circuit board implemented current sensors.

[0004] Background

[0005] Current sensors detect and measure an electrical current passing through a conductor. They are used in many different applications, for example, to provide accurate current measurement in utility meters.

[0006] One type of current sensor uses a shunt resistor in series with the current carrying conductor. The voltage drop across the resistor may be measured and, through knowledge of the resistance of the shunt, the current through the resistor may be calculated. However, at higher currents the temperature of the shunt may increase, changing the resistance of the shunt, and therefore providing an inaccurate current measurement. Further, as the shunt is located directly in the measured current path, isolating circuitry may be required between the shunt and the sensitive measurement and processing electronics.

[0007] Another type of current sensor uses an electromagnetic transducer to detect changes in a magnetic field generated by the current carrying conductor. These rate-of-change of field current sensors, for example Rogowski coils, do not require any physical connection to the current carrying conductor, and are therefore isolated from the current carrying conductor without the need for any further isolating componentry.

[0008] However, as the rate-of-change of field sensor relies on the coupling of magnetic fields, they are susceptible to interference generated by other changing magnetic fields in the vicinity of the sensor. For example, a second current carrying conductor, which is not the target of the measurement operation, may pass near the Rogowski coil. There may be some coupling of the magnetic field generated by this second current carrying conductor into the Rogowski coil, affecting the measurement accuracy of the coil.

[0009] A major challenge with Rogowski coils is this sensitivity to electrostatic or capacitive coupling from nearby AC conductors. Electrostatic coupling from nearby AC conductors is particularly problematic for sensors, such as PCB implemented current sensors, where the gain may be low. This results in a very small erroneous signal, picked up from nearby AC conductors, being significant and having an impact on the SNR of the sensor. For example, in a utility meter, electrostatic coupling may be prevalent due to the positioning of the AC bus bar which carries the current to be measured, but also carries the phase voltage which is typically 240V. With electrostatic coupling the voltage on the bus bar couples into the coil through stray capacitance, and because of the high voltage of the conductor only a small stray capacitance can result in an erroneous signal in the sensor.

[0010] Further, due to a low number of turns or small turn area, the output of a Rogowski coil may have a small amplitude. This makes it particularly susceptible to external noise sources such as electrostatic coupling.

[0011] Increasing the number of turns also improves the smallest signal that can be practically measured, because there is a finite noise in the readout (thermal, flicker, quantisation) electronics and the larger the signal the better the Signal-Noise Ratio (SNR) for a similar electronic cost (power, area, cost). This may be particularly important in constrained applications where there is a limit to the size of the coil, or the conductor size or the power consumption of the electronics.

[0012] There is a need to provide a current sensor implemented on a substrate with a reduced noise in the signal output, whilst also maximising the number of turns or loops of each coil of the current sensor to maximise the induced signal amplitude.

[0013] Summary

[0014] According to a first aspect of the present disclosure, there is provided a current sensor, the current sensor comprising: a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path; a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path; wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops, the first plurality of loops and the second plurality of loops being formed using a plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using a first plurality of outer circumference vias positioned at a first radial distance from a centre of the measurement coils and a first plurality of inner circumference vias; wherein the first measurement coil is coupled to the second measurement coil at a turn-around via, the turn-around via being positioned at a second radial distance from the centre of the measurement coils, the second radial distance being different to the first radial distance.

[0015] According to a second aspect of the present disclosure, there is provided a current sensor, the current sensor comprising: a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path; and a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path; wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops, the first plurality of loops and the second plurality of loops being formed using a plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using a first plurality of outer circumference vias and a first plurality of inner circumference vias; wherein the first measurement coil is coupled to the second measurement coil at a turn-around via; wherein a majority of loops of the first plurality of loops and the second plurality of loops enclose a first loop area; wherein a loop of the first plurality of loops that is coupled to the turnaround via and a loop of the second plurality of loops that is coupled to the turn-around via enclose a second loop area.

[0016] According to a third aspect of the present disclosure, there is provided a current sensor, the current sensor comprising: a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path, the first measurement coil comprising a first end, a second end and a first plurality of loops; and a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path, the second measurement coil comprising a first end, a second end and a second plurality of loops; wherein the first end of the first measurement coil is coupled to a first terminal, the second end of the first measurement coil is coupled to the first end of the second measurement coil, and the second end of the second measurement coil is coupled to a second terminal, wherein a majority of the plurality of loops of the first measurement coil and the second measurement coil enclose a first loop area, wherein a loop of the first plurality of loops at the second end of the first measurement coil and a loop of the second plurality of loops at the first end of the second measurement coil each enclose a second loop area, wherein a loop of the first plurality of loops coil at the first end of the first measurement coil and a loop of the second plurality of loops at the second end of the second measurement coil each enclose a third loop area, wherein the average of the second loop area and the third loop area is the same as the first loop area.

[0017] According to a fourth aspect of the present disclosure, there is provided a current sensor, the current sensor comprising: a substrate comprising a first layer and a second layer; a first measurement coil provided on the substrate, the first measurement coil comprising a first end; a second measurement coil provided on the substrate, the second measurement coil comprising a first end; and a connection arrangement, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate, wherein the first end of the first measurement coil is for coupling to a first circuit via the first connection conductor; and a second connection conductor provided on the second layer of the substrate, wherein the first end of the second measurement coil is for coupling to a second circuit via the second connection conductor, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate.

[0018] According to a fifth aspect of the present disclosure, there is provided a connection arrangement for a printed circuit board, PCB, implemented current sensor, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate wherein the first connection conductor is for coupling the PCB implemented current sensor to a first circuit; and a second connection conductor provided on the second layer of the substrate, wherein the second connection conductor is for coupling the PCB implemented current sensor to a second circuit, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor in a plane that is perpendicular to a surface of the substrate.

[0019] According to a sixth aspect of the present disclosure, there is provided a current sensor, the current sensor comprising: a substrate comprising a first layer and a second layer; a first measurement coil provided on the substrate, the first measurement coil comprising a first end; a second measurement coil provided on the substrate, the second measurement coil comprising a first end; a third measurement coil provided on the substrate, the third measurement coil comprising a first end; a fourth measurement coil provided on the substrate, the fourth measurement coil comprising a first end; a connection arrangement, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate, wherein the first end of the first measurement coil is for coupling to a first circuit via the first connection conductor; and a second connection conductor provided on the second layer of the substrate, wherein the first end of the second measurement coil is for coupling to a second circuit via the second connection conductor, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate; a third connection conductor provided on the first layer of the substrate, wherein the first end of the third measurement coil is for coupling to the first circuit via the third connection conductor; and a fourth connection conductor provided on the second layer of the substrate, wherein the first end of the fourth measurement coil is for coupling to the second circuit via the fourth connection conductor, wherein the third connection conductor on the first layer is substantially aligned with the fourth connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate. Brief Description of the Drawings

[0020] Aspects of the disclosure will now be described by way of example only and with reference to the accompanying drawings, wherein like reference numerals refer to like parts, and wherein :

[0021] Figure 1 is a schematic representation of a Rogowski coil;

[0022] Figure 2a is a schematic representation of a first measurement coil and first return coil in accordance with the invention;

[0023] Figure 2b is a schematic representation of a second measurement coil and second return coil in accordance with the invention;

[0024] Figure 2c is a schematic representation of the first and second measurement and return coils of Figures 2a and 2b in accordance with the invention;

[0025] Figure 3a is a simplified schematic representation of the coils of figure 2a;

[0026] Figure 3b is a simplified schematic representation of the coils of figure 2b;

[0027] Figure 3c is a simplified schematic representation of the coils of Figure 2c;

[0028] Figure 4 is a PCB layout of a current sensor implemented on two layers of a substrate;

[0029] Figure 5a is a PCB layout of a current sensor implemented on four layers of a substrate with a pattern that repeats every eighth loops;

[0030] Figure 5b is a PCB layout of the first measurement coil and return coil of Figure 5a;

[0031] Figure 5c is a PCB layout of the second measurement coil and return coil of Figure 5a;

[0032] Figure 5d is a three-dimensional view of the PCB layout of Figure 5a;

[0033] Figure 6a is a simplified section of the PCB layout of Figure 5a indicating portions of the first measurement coil;

[0034] Figure 6b is a simplified section of the PCB layout of Figure 5a indicating portions of the second measurement coil;

[0035] Figure 6c is a simplified section of the PCB layout of Figure 5a indicating portions of the first return coil;

[0036] Figure 6d is a simplified section of the PCB layout of Figure 5a indicating portions of the second return coil;

[0037] Figure 6e is a simplified section of the PCB layout of Figure 5a;

[0038] Figure 7 is a simplified section of the PCB layout of Figure 5a indicating turns of all the coils;

[0039] Figure 8a is a PCB layout of a current sensor implemented on four layers of a substrate with a pattern that repeats every four loops;

[0040] Figure 8b is a PCB layout of the first measurement coil and return coil of Figure 8a;

[0041] Figure 8c is a PCB layout of the second measurement coil and return coil of Figure 8a;

[0042] Figure 8d is a three-dimensional view of the PCB layout of Figure 8a;

[0043] Figure 9a is a simplified section of the PCB layout of Figure 8a indicating portions of the first measurement coil;

[0044] Figure 9b is a simplified section of the PCB layout of Figure 8a indicating portions of the second measurement coil; Figure 9c is a simplified section of the PCB layout of Figure 8a indicating portions of the first return coil;

[0045] Figure 9d is a simplified section of the PCB layout of Figure 8a indicating portions of the second return coil;

[0046] Figure 9e is a simplified section of the PCB layout of Figure 8a;

[0047] Figure 10 is a simplified section of the PCB layout of Figure 8a indicating turns of all the coils;

[0048] Figure 11 is a PCB layout of a current sensor with staggered vias;

[0049] Figure 12 is a PCB layout showing the coupling of the start and end points of the coils;

[0050] Figure 13 is a PCB layout showing compensation 180degrees from the start and end points of the coils;

[0051] Figure 14a is a PCB layout indicating the coupling of the coils to output terminals;

[0052] Figure 14b is a three-dimensional view of the PCB layout of Figure 14a;

[0053] Figure 15a is a PCB layout of a loop or turn of a coil;

[0054] Figure 15b is a three-dimensional view of the loop or turn of Figure 15a;

[0055] Figure 16 is a stack-up or layer diagram of a substrate or PCB;

[0056] Detailed Description

[0057] Known Rogowski coils may be negatively impacted by both electrostatically and magnetically coupled noise. This noise may be noise from magnetically coupled noise from current carrying conductors near to the Rogowski coil or electrostatically coupled noise caused by AC voltage carrying conductors near to the Rogowski coil. The noise coupled into a Rogowski coil including multiple coils may be different in each of the differential coils, meaning that it cannot be easily cancelled or removed. If the noise coupled into the multiple coils is the same, then it may be easily cancelled or removed via a differential connection of the coils. In particular, where a subsequent processing stage coupled to the differential output of the coils has a good common mode rejection ratio (CMRR).

[0058] Solutions to remove magnetically coupled noise, for example using a compensation or return conductor, may be difficult to implement in printed circuit board implementations of a Rogowski coil.

[0059] So as to improve the operation of a current sensor, four measurement coils or Rogowski coils, may be implemented on a single printed circuit board or substrate. The measurement coils act to surround a conductor under test (also referred to as a current carrying conductor). The output voltage of a Rogowski coil is proportional to the number of loops or turns of the measurement coil. Providing four coils increases the number of turns and therefore the sensitivity of the system. Throughout the description, the use of "loop" and "turn" may be used interchangeably and should be understood to mean the same thing - a portion of the coil that encloses an area. Each measurement coil forms a toroidal coil surrounding the conductor under test and is formed of a number of loops or turns which wind to form the coil from a first end or terminal of each coil to a second end or terminal of each coil.

[0060] The measurement coils may comprise two measurement coils that progress in a first direction around the conductor under test, and two measurement coils that progress in a second direction, opposite to the first direction, around the conductor under test. The measurement coils may follow substantially the same path, or adjacent paths around the conductor. By following the same path, the current sensor balances electrostatic coupling from a noise voltage external to the coils. The same electrostatic coupling is present in all the coils that follow substantially the same path, resulting in a common mode signal that can be easily removed, improving system performance when measuring low current without the need to utilise a shield.

[0061] The current sensor acts to reject external longitudinal electromagnetic fields. These may be caused by external noise generating conductors that are in substantially the same direction as the conductor under test, but external to the current sensor. As the measurement coils are provided in a substantially circular arrangement around the conductor under test, a nearer part of the coil to the longitudinal electromagnetic field may be subject to a greater electromagnetic field strength over a smaller area. A further part of the coil (180 degrees around the coil) may be subject to a lower electromagnetic field strength over a larger area. This results in the coupled noise in these two sections of the coil being of the same size, but of opposite sign. As such, the noise caused by the longitudinal electromagnetic field cancels due to the shape of the coils.

[0062] The current sensor also acts to reject external transverse electromagnetic fields. These may be caused by external noise generating conductors that are perpendicular to a conductor under test, for example across the surface of the substrate on which the measurement coils are formed. If two of the current measurement coils travel from 0 degrees to 360 degrees in the same direction, the same noise from the transverse noise source couples into both the first and second measurement coil. Further, if the other two measurement coils travel in the opposite direction, from 360 degrees to 0 degrees, the same noise from the transverse noise source couples into both the third and fourth measurement coils. This coupled noise may then be simply cancelled.

[0063] Rejecting both transverse and lateral external field sources reduces crosstalk from the external field source into the current measurement signal, allowing easy integration of the current sensor into harsh environments. PCB implemented measurement coils comprising four measurement coils are difficult to implement without a large number of vias. For example, the measurement coils may require more than two vias coupling conductors on different layers for each turn or loop of the measurement coil. This increases manufacturing difficulty, and due to the tolerances in manufacturing each via, may lead to mismatch in the loop area and mismatch in the noise or signal coupling into each coil. By providing the measurement coils with two vias per turn or loops, manufacturing complexity is reduced and coil performance is improved.

[0064] Each loop or turn of each measurement coil may be provided substantially in a unique plane, such as a radial plane. A measurement coil comprises a plurality of circumferentially progressing elements and a plurality of radially progressing elements. The circumferentially progressing elements provide progression around the PCB, substrate or conductor, whilst the radially progressing elements provide progression in a radial direction from a centre of the substrate or measurement coils. Together with the vias, these conductors form the loops of the measurement coils.

[0065] By locating each turn or loop in a unique plane, the radially progressing elements of the coils do not clash with one another. Clashing may be defined as the same location being required for conductors of more than one coil on the same layer. The layers of each measurement coil, or each turn or loop of each measurement coil, may be selected such that the circumferentially progressing conductors do not clash with one another, whilst requiring only two vias per turn or loop.

[0066] PCB implemented current sensors, comprising any number of measurement coils, require a connection to processing or measurement circuitry that is either on the PCB or external to the PCB. This connection or hookup region may change or modify the performance of the coil, acting as an extra region for noise pickup and resulting in changes in the loop area.

[0067] So that the measurement coils may progress substantially around the substrate, providing improved rejection of longitudinal external fields, the start and end of each measurement coil may be located as close to one another as possible - preferably at the same angular position. To achieve this, one of the vias may be offset in a radial direction from a radial position at which the rest of the vias are located. This may be described as in-setting or offsetting the via. However, this results in the area enclosed by a loop at the start and end of the coil being different to the average area enclosed by a loop of the measurement coil. To counteract this, the first and last loops may be coupled to vias with different positions, such that the average loop area of the first and last loops is substantially the same as the average loop area of all other loops of the coil. Alternatively, the loops 180 degrees around the coil from the first and last loop may comprise a loop area different to the average loop area, such that the first loops, last loops and loops positioned at substantially 180 degrees have the same loop area.

[0068] Further, the hookup conductors may be provided on different layers of the substrate, in substantially the same plane as one another. This results in the noise pickup in the conductors cancelling out with one another.

[0069] Figure 1 is a diagram of a known Rogowski coil. So as to measure the current I(t) flowing through a current carrying conductor 100, a measurement coil 102 is arranged such that the current carrying conductor 100 passes through the measurement coil. The measurement coil 102 is wound as a helix, such that a loop or turn of the helix encloses a cross-sectional area 104, A. The current carrying conductor 100 may be, for example, a busbar.

[0070] As the current I(t) in the current carrying conductor 100 changes, the field generated by the current also changes. The positioning of the measurement coil causes a voltage to be induced in the measurement coil 102 which is proportional to the rate of change of current, dl / dt. Therefore, integrating the output v(t) of the measurement coil provides a value proportional to the current. Each turn or loop of the coil forms a measurement area 104 in a plane perpendicular to the progression of the current carrying conductor.

[0071] However, the voltage induced in the measurement coil may be affected by external conductors which the user is not intending to measure. As well as the loops of the coil which form the plurality of measurement areas 104, the progression of the coil itself also effectively forms a single loop in the plane of the current carrying conductor. To address the coupling of magnetic fields into this single loop, a compensation conductor may be included.

[0072] The Rogowski coil of Figure 1 is a single-ended Rogowski coil, including one measurement coil 102 which progresses around the conductor 100. A current sensor may include more than one measurement coil, and be arranged to provide a differential output.

[0073] For example, figures 2a, 2b and 2c show diagrams of a differential rate of change of current sensor 200 for measuring the current in a current carrying conductor 100. The rate of change of current sensor includes four current measurement coils, which may be referred to as two forward and two return coils. Figure 2c shows the complete rate of change of current sensor, including the first measurement coil, the second measurement coil and their respective return coils. Figure 2a shows a first measurement coil 204 and its respective first return coil 206. Figure 2b shows a second measurement coil 208, and its respective second return coil 210. The return coils have been referred to as such for clarity, however it should be understood that the return coils act to measure the current in the current carrying conductor in the same manner as the forward measurement coils. Throughout the description, the coils may be referred to as measurement coils. Measurement coils may refer to measurement coils progressing in a first direction and return coils may refer to measurement coils that progress in a second direction, where the second direction is opposite to the first direction. The return coils may therefore also be considered to be measurement coils, or they may be considered to be part of their respective measurement coil. Further, they may be described as return or reverse measurement coils.

[0074] The first measurement coil 204 and second measurement coil 208 may be referred to as such, whilst the first return coil 206 may be referred to as a third measurement coil and the second return coil 210 may be referred to as a fourth measurement coil. However, any suitable numbering of the coils may be used to distinguish the coils.

[0075] The two return coils 206, 210 are secondary measurement coils which may be referred to as the return or reverse coil.

[0076] The first end of first measurement coil 204 begins at terminal or node 212 and progresses or travels in an anti-clockwise direction around the path for the current carrying conductor 100 (or in an alternative implementation, in a clockwise direction), terminating at second end or node 214. First return coil 206 travels or progresses in the opposite direction to the first measurement coil 204 from node 214 to node 216, clockwise around the path for the current carrying conductor or the current carrying conductor 200. The first end 214 of the first return coil 206 is coupled to the second end 214 of the first measurement coil 204. A rate of change of current sensor may be provided that includes a measurement coil and return coil, so as to provide an increased number of coil turns whilst still providing cancellation of external transverse magnetic fields.

[0077] The first end of second measurement coil 208 begins at terminal 218 and progresses or travels in an anticlockwise direction around the path for current carrying conductor 100 (or in an alternative implementation, in a clockwise direction), terminating at second end or node 220. Second return coil 210 travels or progresses in the opposite direction to the second measurement coil 208 from node 220 to node 222, clockwise around the path for the current carrying conductor 100. The first end 220 of the first return coil 206 is coupled to the second end 220 of the second measurement coil 208.

[0078] Whilst the first measurement coil 204 and second measurement coil 208 are described as travelling or progressing in an anticlockwise direction, they may alternatively progress in a clockwise direction. The first return coil 206 and the second return coil 210 progress in a substantially opposite direction to the first measurement coil 204 and second measurement coil 208, and would therefore progress in an anti-clockwise direction when the measurement coils progress in a clockwise direction.

[0079] The first measurement coil 204 and the second measurement coil 208 may therefore be referred to as forward measurement coils and the first return coil 206 and the second return coil 210 may be referred to as reverse, opposite or backwards measurement coils. This is because the first measurement coil 204 and the first return coil 206 progress in opposite circumferential directions. The second measurement coil 208 and the second return coil 210 progress in opposite circumferential directions.

[0080] In this implementation the measurement coils progress in the same circumferential direction relative to each other, however, the coils may alternatively progress in the opposite direction relative to each other. However, if the measurement coils progress in opposite directions, the coils will be more susceptible to electrostatic coupling as the capacitive coupling from each coil to the interferer might not match. This is not desirable. The schematic diagram of figures 2a-2c show both the first measurement coil 204 and the second measurement coil 208 progressing substantially around the path for the current carrying conductor 100, so as to surround the path. Similarly, return coils 206, 210 may progress substantially around the path for the current carrying conductor 100, so as to surround the path.

[0081] As well as the direction that the measurement and return coils progress around the conductor 100 or substrate, each turn or loop of each coil may be considered to progress in a certain direction. For example, when the coils are viewed from an angle through the toroid formed by the coils, the turns or loops may be seen to progress in a clockwise or anticlockwise direction from the respective first end.

[0082] Each measurement coil includes a number of turns or loops. When viewed through the toroidal shape formed by the coils, the turns or loops of each measurement coil are arranged to progress in either a clockwise direction or an anti-clockwise direction from the first terminals or ends of each measurement coil.

[0083] The first measurement coil 204 has turns or loops that progress in a clockwise direction from the first end 212 of the first measurement coil 204. Similarly, the first return coil 206 has turns or loops that progress in a clockwise direction from the first end of the first return coil. The second measurement coil 208 and the second return coil 210 have turns or loops that progress from their respective first ends in an opposite direction to the progression of the turns or loops of the first measurement and return coils. As such, the second measurement coil 208 has turns or loops that progress in an anti-clockwise direction from the first end 218 of the second measurement coil 208. The second return coil 210 has turns or loops that progress in an anti-clockwise direction from a first end 220 of the second return coil 210. This is indicated by the polarity markers on Figures 3a-3c. This results in the first measurement coil having an opposite polarity to the second measurement coil and the first return coil having an opposite polarity to the second return coil. This opposite winding polarity is shown by the polarity markers of Figures 3a-3c

[0084] For example, the first measurement coil 204 comprises a loop 226. Loop 226 progresses in a clockwise direction from the first end 212 of the first measurement coil 204 when viewed through the toroid formed by the first measurement coil 204. Whilst only one loop is labelled, all loops of the first measurement coil progress in this same clockwise direction.

[0085] The first return coil 206 comprises a loop 228. Loop 228 progresses in a clockwise direction from the first end 214 of the first return coil 206 when viewed through the toroid formed by the first return coil 206. Whilst only one loop is labelled, all loops of the first return coil 206 progress in this same clockwise direction.

[0086] In contrast, the second measurement coil 208 comprises a loop 230. Loop 230 progresses in an anti-clockwise direction from the first end 218 of the second measurement coil 208 when viewed through the toroid formed by the second measurement coil 208. Whilst only one loop is labelled, all loops of the second measurement coil 208 progress in this same anti-clockwise direction.

[0087] The second return coil 210 comprises a loop 232. Loop 232 progresses in an anti-clockwise direction from the first end 220 of the second return coil 210 when viewed through the toroid formed by the second return coil 210. Whilst only one loop is labelled, all loops of the second return coil 210 progress in this same anti-clockwise direction.

[0088] Alternatively, the loops of the first measurement coil 204 and first return coil 206 may progress in an anti-clockwise direction and the loops of the second measurement coil 208 and second return coil 210 may progress in a clockwise direction.

[0089] Winding the measurement and return coils in this manner results in a positive voltage being induced in the first measurement coil 204 and a negative voltage being induced in the second measurement coil 208. These induced voltages will difference to create a differential signal that represents the changing magnetic field from the conductor running through the centre of the coils. The differential voltage is with respect to the common mode point that joins the first and second coils. This common mode voltage may be at electronic ground of the readout attached to the coil, or at a voltage suitable for the electronics Whilst the first measurement coil 204 and first return coil 206 are described as having a clockwise turn progression and the second measurement coil 208 and second return coil 210 are described as having an anti-clockwise turn progression, it should be appreciated that this implementation may also be swapped. As such, the first measurement coil 204 and first return coil 206 may have an anti-clockwise turn progression and the second measurement coil 208 and second return coil 210 may have a clockwise turn progression.

[0090] Simplified circuit diagrams of figures 2a-2c are shown in figures 3a-3c. Notably, the second end 216 of the first return coil 206 may be coupled to the second end 222 of the second return coil 210. The sensor may further be coupled to signal processing circuitry. The first end 212 of the first measurement coil may be coupled to a first or positive output terminal 324. The first end 218 of the second measurement coil 208 may be coupled to a second or negative output terminal 326. The second end 216 of the first return coil 206 and the second end 222 of the second return coil 210 may be coupled to a reference voltage or ground terminal 328. The first output terminal 324 and the second output terminal 326 are differential output terminals that may be coupled to signal processing circuitry or further processing circuitry.

[0091] Figures 2 and 3 may be seen as simplified diagrams of any of the substrate or PCB implementations of current sensors described throughout this application.

[0092] Figure 4 is a printed circuit board implementation 402 of the current sensor 200 implemented across two layers of a circuit board or substrate. The current sensor includes a plurality of outer vias 404 which are arranged around three concentric circumferences. The current sensor further comprises a plurality of inner vias 406 arranged around two concentric circumferences. The current sensor includes conductive traces 408 arranged across the first layer of the substrate and the second layer of the substrate, connected by vias from both the outer vias 404 and the inner vias 406. The traces on the first layer and the second layer are aligned in radial planes, and as such the traces on the second layer are not visible in Figure 4.

[0093] Each coil of the current sensor may be considered to be a helical coil or winding, comprising a number of turns or loops. The voltage signal proportional to a rate of change of current induced in the coil is proportional to the number of turns or loops. To provide a high number of measurement coil turns or loops, which may be important to increase measurement coil sensitivity, the inner 406 and outer vias 408 are arranged in multiple circles. Each turn of a measurement coil or a return coil requires four vias, including one via from the inner vias 406 and three vias from the outer vias 404. Routing the coils such that the loops or turns are wound in a particular direction to generate voltages of the correct polarity is difficult to implement in the system of Figure 4, as conductors in some locations block each other in the advancement section of the coil. The additional vias shown in Figure 4 are therefore used to overcome this blocking.

[0094] It may be desirable to reduce the required number of vias, to provide simpler routing of the conductive traces 408 that make up the current sensor. A reduced number of vias reduces the overall error in the PCB implementation of the measurement coil and return coil caused by errors in the drilling process due to drilling tolerances. The number of vias per spoke may adversely affect the cost of manufacturing as each via involves a manufacturing operation. Further, reducing the number of vias increases the coil sensitivity or output voltage, as additional vias may subtract from the loop area of the coil.

[0095] Four-Layer Eight-Turn Current Sensor

[0096] A current sensor may be implemented on a substrate comprising four layers, with four current measurement coils arranged to progress at least partially around a path for a conductor through the substrate. Each measurement coil may be implemented across all four layers of the substrate, such that it comprises measurement conductors on each layer of the substrate. The measurement conductors of each loop of each measurement coil may be located in a unique radial plane to the measurement conductors of each of the other measurement coils. This prevents the turns or loops clashing with one another, and only two vias are required per turn.

[0097] As each measurement coil is implemented across all four layers, an alternating arrangement of loops is provided for each measurement coil - for example a first loop provided across two layers and a second loop provided across the other two layers. These loops may be provided in a repeating pattern, such that the pattern formed by the four measurement coils repeats every eight turns or loops. Alternatively, the pattern may be repeated any multiple of eight loops.

[0098] Providing each coil across all four layers improves the matching of coupling of external fields into the four measurement coils - as each coils has the same average proportion of turns on each layer of the substrate. This means that the distance to external conductors is, on average, the same for all four coils.

[0099] Figure 5a shows a printed circuit board, PCB, implementation 500 of the current sensor 200 shown in Figures 2a-2c, with the current sensor measurement coils implemented across four layers of the PCB. The current sensor 500 comprises a substrate 502 comprising four layers.

[0100] The current sensor 500 includes a first measurement coil 204, a first return coil 206, a second current measurement coil 208 and a second return coil 210. The substrate 502 comprises a first plurality of vias 504 arranged around an inner circumference of the first measurement coil 204 and the second measurement coil 208. The substrate comprises a second plurality of vias 506 arranged around an inner circumference of the first return coil 206 and the second return coil 210. The first plurality of vias 504 is shown arranged around a different circumference to the second plurality of vias 506, such that the first and second plurality of vias are staggered or arranged around concentric circumferences or circles. Alternatively, the first plurality of vias 504 and the second plurality of vias 506 may be arranged around the same circumference.

[0101] The substrate 502 further comprises a third plurality of vias 508 arranged around an outer circumference of the first measurement coil 204 and the second measurement coil 208. The substrate comprises a fourth plurality of vias 510 arranged around an outer circumference of the first return coil 206 and the second return coil 210. The third plurality of vias 508 and the fourth plurality of vias 510 are shown in Figure 5a as being arranged around the same circumference. However, alternatively, the third plurality of vias 508 and the fourth plurality of vias 510 may be arranged around different circumferences, such that the third and fourth plurality of vias are staggered or arranged around concentric circumferences or circles.

[0102] The current sensor 500 includes a conductor 100 for carrying a current to be measured by the first current measurement coil 204 and the second current measurement coil 206. The conductor 100 is implemented along a path 522 of the substrate 502. The path 522 may be an aperture for receiving the conductor 100. Alternatively, the conductor 100 may be a conductive trace running through the substrate, with no aperture present. The conductor 100 or path for the conductor 522 is located centrally, such that the first measurement coil 204, second measurement coil 208, first return coil 206 and second return coil 210 are formed as circles around or centred on the conductor 100. The conductor 100 may be any conductor suitable for carrying a current to be measured by the current sensor.

[0103] Whilst the vias are described as being arranged around circumferences of the coils, they may also be considered to be formed around circumferences or in circles around a point centred on the conductor 100 or the path for the conductor 522. It will also be appreciated that the coils may not be perfect circles or may be arranged as other shapes around the conductor, although if they are not provided in a circular arrangement, they would not benefit from the same rejection from transverse fields from a neighbouring external conductor.

[0104] The first current measurement coil 204, the second current measurement coil 208, the first return coil 206 and the second return coil 210 are implemented across the four layers of the substrate, comprising conductors or conductive traces on the different layers of the substrate. The conductors on the different layers are coupled to one another using the plurality of vias. A legend is provided on the figure, wherein the conductors on different layers of the substrate 502 are represented using different line formats.

[0105] The first plurality of vias 504 and the third plurality of vias 508 are used to couple conductors or conductive traces of the first measurement coil 204 and the second measurement coil 208. The second plurality of vias 506 and the fourth plurality of vias 510 are used to couple conductors or conductive traces of the first return coil 206 and the second return coil 210. The vias allows loops or turns to be formed for the measurement and return coils which span multiple layers of the substrate. The first plurality of vias 504 and the third plurality of vias 508 form the turns or loops of the first measurement coil 204 and the second measurement coil 208. The second plurality of vias 506 and the fourth plurality of vias 510 form the turns or loops of the first return coil 206 and the second return coil 210.

[0106] Each of the coils of the current sensor 500 includes conductors on all four layers of the substrate. Each layer of the substrate 502 comprises a plurality of measurement conductors. A first plurality 514 of measurement conductors are located on a first layer of the substrate 502. A second plurality 516 of measurement conductors are located on a second layer of the substrate 502. A third plurality 518 of measurement conductors are located on a third layer of the substrate 502. A fourth plurality 520 of measurement conductors are located on a fourth layer of the substrate 502. The measurement conductors are located in radial planes from the conductor 100 or path for the conductor.

[0107] The third plurality of measurement conductors 518 and the fourth plurality of measurement conductors 520 cannot be seen in Figure 5a, as the first plurality of measurement conductors 514 and the second plurality of measurement conductors 516 are located in the same plane as the third plurality of measurement conductors 518 and the fourth plurality of measurement conductors 520.

[0108] Figure 5d shows a three-dimensional side view of the current sensor 500, in which the third plurality of measurement conductors 518 and the fourth plurality of measurement conductors 520 can be seen.

[0109] The substrate 502 further comprises a plurality of circumferential progression conductors 512. The circumferential progression conductors are arranged to provide circumferential progression for the measurement coils and for the return coils around the conductor 100 or path for the conductor 522. The circumferential progression conductors may be referred to as an advancement region of the substrate 502, as they allow the coils to progress or advance around the substrate 502, surrounding the conductor 100. Figure 5b shows the current sensor 500 of Figure 5a, with only the first measurement coil 204 and the first return coil 206 present. Figure 5c shows the current sensor 500 of Figure 5a, with only the second measurement coil 208 and the second return coil 210 present.

[0110] Figures 6a-6e shows a simplified (as a linear progression) subsection of the conductive traces and vias of the measurement and return coils of Figures 5a-5d. Figure 6a has reference numerals related to parts of the first measurement coil 204. Figure 6b has reference numerals related to parts of the second measurement coil 208. Figure 6c has reference numerals related to parts of the first return coil 206. Figure 6d has reference numerals related to parts of the second return coil 210.

[0111] Considering Figure 6a, the first measurement coil 204 includes a plurality of loops or turns.

[0112] A first turn or loop of the first current measurement coil 204 comprises a circumferential progression conductor 602 on the fourth layer of the substrate. A first end of the circumferential progression conductor 602 is coupled to a second end of a measurement conductor 604 of the fourth plurality of measurement conductors 520 on the fourth layer of the substrate. A first end of measurement conductor 604 is coupled to a via 606 of the first plurality of vias 504. A first end of a measurement conductor 608 of the first plurality of measurement conductors 514 on the first layer of the substrate is coupled to the via 606. A second end of the measurement conductor 608 is coupled to a first end of a circumferential progression conductor 610 on the first layer of the substrate. A second end of the circumferential progression conductor 610 is coupled to a via 612 of the third plurality of vias 508. The first turn or loop begins at the outer circumference of the measurement coil, progresses on the fourth layer to the inner circumference of the measurement coil, switches to the first layer and then progresses to the outer circumference of the measurement coil on the first layer. In this way, a turn or loop is formed across the fourth and first layer of the substrate.

[0113] The first ends of the respective conductors are closer to the inner circumference of the coil, or closer to the current carrying conductor 100 or path for the current carrying conductor 522. Whilst the vias are described as inner and outer circumferences, it is clear that the vias may be provided in a number of different shapes, with the inner vias closer to the conductor 100 or path 522, and the outer vias further from the conductor 100 or path 522.

[0114] A second turn or loop of the first current measurement coil 204 comprises a circumferential progression conductor 614 on the third layer of the substrate. A first end of the circumferential progression conductor 614 is coupled to a second end of a measurement conductor 616 of the third plurality of measurement conductors 518 on the third layer of the substrate. A first end of the measurement conductor 616 is coupled to a via 618 of the first plurality of vias 504. A first end of a measurement conductor 620 of the second plurality of measurement conductors 516 on the second layer of the substrate is coupled to the via 618. A second end of the measurement conductor 620 is coupled to a first end of a circumferential progression conductor 622 on the second layer of the substrate. A second end of the circumferential progression conductor 622 is coupled to a via 624 of the third plurality of vias 508. The second turn or loop of the first measurement coil 204 begins at the outer circumference of the measurement coil, progresses on the third layer to the inner circumference of the measurement coil, switches to the second layer and then progresses to the outer circumference of the measurement coil on the second layer. In this way, a turn or loop is formed across the third and second layer of the substrate.

[0115] The first turn or loop of the first measurement coil is coupled to the second turn or loop of the first measurement coil 204 using the via 612 of the third plurality of vias 508. The pattern of the first measurement coil 204 repeats every two turns or loops, The first measurement coil comprises a plurality of loops, for example n loops, numbered 1 to n. The first measurement coil may therefore be considered to comprise a plurality of even numbered loops and a plurality of odd loops. As such the first loop of the first measurement coil 204 may be considered an even loop and the second loop of the first measurement coil 204 may be considered an odd loop (or vice versa). All the even numbered turns of the first measurement coil are implemented on the fourth and first layers, and all the odd turns of the first measurement coil are implemented on the third and second layers (or vice versa).

[0116] Whilst the progression of the loops of the first measurement coil have been described as travelling from the left side of Figure 6a to the right side of Figure 6a, it should be appreciated that this is for ease of description only, and does not specifically describe the direction of travel around the circumference from the starting point of the coil. A voltage induced in a loop of the first measurement coil 204 by the rate of change of a current in the conductor 100 creates a cumulative voltage across the measurement coil when all the loops that are joined together are considered. The progression of the loops with respect to Figures 6a-6d have been described in a single direction, however the progression of the loops may be in a clockwise or anti-clockwise direction, as described previously. As such, loops of the different coils may progress in different or opposite directions.

[0117] Considering Figure 6b, the second measurement coil 208 includes a plurality of loops or turns.

[0118] A first turn or loop of the second current measurement coil 208 comprises a circumferential progression conductor 626 on the second layer of the substrate. A first end of the circumferential progression conductor 626 is coupled to a second end of a measurement conductor 628 of the second plurality of measurement conductors 516 on the second layer of the substrate. A first end of measurement conductor 628 is coupled to a via 630 of the first plurality of vias 504. A first end of a measurement conductor 632 of the fourth plurality of measurement conductors 520 on the fourth layer of the substrate is coupled to the via 630. A second end of the measurement conductor 632 is coupled to a first end of a circumferential progression conductor 634 on the fourth layer of the substrate. A second end of the circumferential progression conductor 634 is coupled to a via 636 of the third plurality of vias 508. The first turn or loop begins at the outer circumference of the measurement coil, progresses on the second layer to the inner circumference of the measurement coil, switches to the fourth layer and then progresses to the outer circumference of the measurement coil on the fourth layer. In this way, a turn or loop is formed across the second and fourth layers of the substrate.

[0119] A second turn or loop of the second current measurement coil 208 comprises a circumferential progression conductor 638 on the first layer of the substrate. A first end of the circumferential progression conductor 638 is coupled to a second end of a measurement conductor 640 of the first plurality of measurement conductors 514 on the first layer of the substrate. A first end of the measurement conductor 640 is coupled to a via 642 of the first plurality of vias 504. A first end of a measurement conductor 644 of the third plurality of measurement conductors 518 on the third layer of the substrate is coupled to the via 642. A second end of the measurement conductor 644 is coupled to a first end of a circumferential progression conductor 646 on the third layer of the substrate. A second end of the circumferential progression conductor 646 is coupled to a via 648 of the third plurality of vias 508. The second turn or loop of the second measurement coil 208 begins at the outer circumference of the measurement coil, progresses on the first layer to the inner circumference of the measurement coil, switches to the third layer and then progresses to the outer circumference of the measurement coil on the third layer. In this way, a turn or loop is formed across the first layer and the third layer of the substrate.

[0120] The first turn or loop of the second measurement coil 208 is coupled to the second turn or loop of the second measurement coil 208 using the via 636 of the third plurality of vias 508. The pattern of the second measurement coil 208 repeats every two turns or loops. The second measurement coil 208 comprises a plurality of loops, for example n loops, numbered 1 to n. The second measurement coil may therefore be considered to comprise a plurality of even numbered loops and a plurality of odd loops. As such the first loop of the second measurement coil 208 may be considered an even loop and the second loop of the second measurement coil 208 may be considered an odd loop (or vice versa). All the even numbered turns of the second measurement coil are implemented on the second and fourth layers, and all the odd turns of the second measurement coil are implemented on the first and third layers (or vice versa). Considering Figure 6c, the first return coil 206 includes a plurality of loops or turns.

[0121] A first turn or loop of the first return coil 206 comprises a circumferential progression conductor 674 on the second layer of the substrate. A first end of the circumferential progression conductor 674 is coupled to a second end of a measurement conductor 676 of the second plurality of measurement conductors 516 on the second layer of the substrate. A first end of measurement conductor 676 is coupled to a via 678 of the second plurality of vias 506. A first end of a measurement conductor 680 of the fourth plurality of measurement conductors 520 on the fourth layer of the substrate is coupled to the via 678. A second end of the measurement conductor 680 is coupled to a first end of a circumferential progression conductor 682 on the fourth layer of the substrate. A second end of the circumferential progression conductor 682 is coupled to a via 684 of the fourth plurality of vias 510. The first turn or loop begins at the outer circumference of the return coil, progresses on the second layer to the inner circumference of the return coil, switches to the fourth layer and then progresses to the outer circumference of the return coil on the fourth layer. In this way, a turn or loop is formed across the second and fourth layers of the substrate.

[0122] A second turn or loop of the first return measurement coil 206 comprises a circumferential progression conductor 686 on the first layer of the substrate. A first end of the circumferential progression conductor 686 is coupled to a second end of a measurement conductor 688 of the first plurality of measurement conductors 514 on the first layer of the substrate. A first end of the measurement conductor 688 is coupled to a via 690 of the second plurality of vias 506. A first end of a measurement conductor 692 of the third plurality of measurement conductors 518 on the third layer of the substrate is coupled to the via 690. A second end of the measurement conductor 692 is coupled to a first end of a circumferential progression conductor 694 on the third layer of the substrate. A second end of the circumferential progression conductor 694 is coupled to a via 696 of the fourth plurality of vias 510. The second turn or loop of the first return coil 206 begins at the outer circumference of the return coil, progresses on the first layer to the inner circumference of the return coil, switches to the third layer and then progresses to the outer circumference of the return coil on the third layer. In this way, a turn or loop is formed across the first layer and the third layer of the substrate.

[0123] The first turn or loop of the first return coil 206 is coupled to the second turn or loop of the first return coil 206 using the via 684 of the fourth plurality of vias 510. The pattern of the first return coil 206 repeats every two turns or loops. The second return coil 210 comprises a plurality of loops, for example n loops, numbered 1-n. The second return coil may therefore be considered to comprise a plurality of even numbered loops and a plurality of odd loops. As such the first loop of the first return coil 206 may be considered an even loop and the second loop of the first return coil 206 may be considered an odd loop (or vice versa). All the even numbered turns of the first return coil are implemented on the second and fourth layers, and all the odd turns of the first return coil are implemented on the first and third layers (or vice versa).

[0124] Considering Figure 6d, the second return coil 210 includes a plurality of loops or turns.

[0125] A first turn or loop of the second return coil 210 comprises a circumferential progression conductor 650 on the fourth layer of the substrate. A first end of the circumferential progression conductor 650 is coupled to a second end of a measurement conductor 652 of the fourth plurality of measurement conductors 520 on the fourth layer of the substrate. A first end of measurement conductor 652 is coupled to a via 654 of the second plurality of vias 506. A first end of a measurement conductor 656 of the first plurality of measurement conductors 514 on the first layer of the substrate is coupled to the via 654. A second end of the measurement conductor 656 is coupled to a first end of a circumferential progression conductor 658 on the first layer of the substrate. A second end of the circumferential progression conductor 658 is coupled to a via 660 of the fourth plurality of vias 510. The first turn or loop begins at the outer circumference of the return coil, progresses on the fourth layer to the inner circumference of the return coil, switches to the first layer and then progresses to the outer circumference of the return coil on the first layer. In this way, a turn or loop is formed across the fourth and first layers of the substrate.

[0126] A second turn or loop of the second return coil 210 comprises a circumferential progression conductor 662 on the third layer of the substrate. A first end of the circumferential progression conductor 662 is coupled to a second end of a measurement conductor 664 of the third plurality of measurement conductors 518 on the third layer of the substrate. A first end of the measurement conductor 664 is coupled to a via 666 of the second plurality of vias 506. A first end of a measurement conductor 668 of the second plurality of measurement conductors 516 on the second layer of the substrate is coupled to the via 666. A second end of the measurement conductor 668 is coupled to a first end of a circumferential progression conductor 670 on the second layer of the substrate. A second end of the circumferential progression conductor 670 is coupled to a via 672 of the fourth plurality of vias 510. The second turn or loop of the second return coil 210 begins at the outer circumference of the return coil, progresses on the third layer to the inner circumference of the return coil, switches to the second layer and then progresses to the outer circumference of the return coil on the second layer. In this way, a turn or loop is formed across the third layer and the second layer of the substrate.

[0127] The first turn or loop of the second return coil 210 is coupled to the second turn or loop of the second return coil 210 using the via 660 of the fourth plurality of vias 510. The pattern of the second return coil 210 repeats every two turns or loops. The second return coil comprises a plurality of loops, for example n loops, numbered 1-n. The second return coil may therefore be considered to comprise a plurality of even numbered loops and a plurality of odd loops. As such the first loop of the second return coil 210 may be considered an even loop and the second loop of the second return coil 210 may be considered an odd loop (or vice versa). All the even numbered turns of the second return coil are implemented on the first and fourth layers, and all the odd turns of the second return coil are implemented on the second and third layers (or vice versa).

[0128] The vias shown in Figures 6a-6e, and in the following figures are depicted as being in straight lines. This is for ease of understanding. The vias may instead follow a circumference, as shown in Figure 5a.

[0129] Figure 6a-6e show a further plurality of outer measurement conductors 698, referenced in Figure 6e. The outer measurement conductors may be coupled between respective circumferential progression conductors of the plurality of circumferential progression conductors 512 and the vias of the third plurality of vias 508 and fourth plurality of vias 510 respectively. These have not been described for simplicity. The outer measurement conductors 698 are optional, and instead the circumferential progression conductors may be directly coupled or connected to the vias of the third plurality of vias 508 and fourth plurality of vias 510. Further, the plurality of circumferential progression elements may be positioned anywhere between the first 504 / second 506 plurality of vias and the third 508 / fourth 510 plurality of vias.

[0130] The circumferential progression conductors may be positioned adjacent to or directly connected to the inner circumference vias 504, 506. The circumferential progression conductors may be positioned adjacent to or directly connected to the outer circumference vias 508, 510. The circumferential progression conductors may be positioned between the inner circumference vias 504, 506 and the outer circumference vias 508, 510, with both ends of the circumferential progression conductors 512 coupled to measurement conductors which are then coupled to the vias.

[0131] As such, the measurement conductors of the first-fourth plurality of measurement conductors may actually be coupled to outer ends or the second ends of the plurality of circumferential progression conductors 512.

[0132] Figure 7 shows a simplified subsection of the conductive traces and vias of the measurement and return coils of Figures 5a-5d. Figure 7 also shows a wider view of the simplified traces of Figures 6a-6e. As shown in Figure 7, the first measurement coil 204 comprises a first turn 702. Adjacent to the first turn 702 of the first measurement coil is a first turn 704 of the second return coil 210, a first turn 706 of the second measurement coil 208, a first turn 708 of the first return coil 206, a second turn 710 of the first measurement coil, a second turn 712 of the second return coil 210, a second turn 714 of the second measurement coil 208 and a second turn 716 of the first return coil 206. The turns of the respective coils are provided in this order in a circumferential direction around the coils. Any other repeating order of the measurement coil loops or turns may be provided on the substrate - for example, the eight loops may be provided in a different order on the substrate.

[0133] The first measurement coil 204, the first return coil 206, the second measurement coil 208 and the second return coil 210 are provided on the substrate in a repeating pattern which repeats every eight adjacent turns or loops. As such, the section 718 of the current sensor comprises eight turns (two turns of each of the measurement and return coils). This section 718 is repeated throughout the current sensor.

[0134] Figures 6a-6e show each measurement coil comprising a first loop on two of the layers of the substrate, with the next, closest, or adjacent loop of that measurement coil being implemented on the other two layers of the substrate. However, it should be understood that this pattern may be repeated with different numbers of measurement coil loops, such that a plurality - for example two, three or five - of loops of each measurement coil may be provided on two of the layers of the substrate, with the next, closest, or adjacent plurality of loops of that measurement coil being implemented on the other two layers of the substrate. This may change how the pattern repeats - such that the pattern formed by the four measurement coils may be repeated any integer multiple of eight turns.

[0135] Put another way, the current sensor 500 may be considered to comprise eight pluralities of loops. The first measurement coil comprises a first plurality of loops formed on the first and fourth layers of the substrate. The second measurement coil comprises a second plurality of loops formed on the second and fourth layers of the substrate. The first return coil comprises a third plurality of loops formed on the second and fourth layers of the substrate. The second return coil comprises a fourth plurality of loops formed on the third and second layers of the substrate.

[0136] The first measurement coil comprises a fifth plurality of loops formed on the second and fourth layers of the substrate. The second measurement coil comprises a sixth plurality of loops formed on the first and third layers of the substrate. The first return coil comprises a seventh plurality of loops formed on the first and third layers of the substrate. The second return coil comprises an eighth plurality of loops formed on the fourth and first layers of the substrate. The pluralities of loops are ordered, such that a turn of the first plurality of loops is followed by or adjacent to in a circumferential direction to a turn of the fourth plurality of loops. This is then followed by a turn of the second plurality of loops; the third plurality of loops; the fifth plurality of loops; the eighth plurality of loops; the sixth plurality of loops and the seventh plurality of loops. Whilst the ordering has been described as starting from the first plurality of loops, it should be appreciated that the start of the repeating pattern may be considered to be any of the plurality of loops.

[0137] The first measurement coil, the second measurement coil, the first return coil and the second return coil are arranged in a repeating interleaved pattern. The repeating interleaved pattern repeats every eight loops or may repeat every integer (N) multiple of eight loops. An eight-loop repeating portion of the repeating interleaved pattern comprises two loops of each of the plurality of loops. Alternatively, where the pattern repeats every integer (N) multiple of eight loops, the repeating portion comprises an integer multiple of eight loops, for example N*8 loops, and N*2 loops of each of the coils.

[0138] Put another way, the first measurement coil, the second measurement coil, the first return coil and the second return are provided on the substrate such that they form a repeating pattern in a circumferential direction around the path.

[0139] A repeating pattern may comprise a "motif", or a portion of the pattern that is repeated a plurality of times. The repeating pattern comprises a plurality of motifs arranged in a repeating manner, wherein each motif of the repeating pattern comprises a loop of the first plurality of loops, a loop of the second plurality of loops, a loop of the third plurality of loops, a loop of the fourth plurality of loops, a loop of the fifth plurality of loops, a loop of the sixth plurality of loops, a loop of the seventh plurality of loops and a loop of the eighth plurality of loops.

[0140] By repeating the loops of the measurement coils in this fashion, with each coil provided across the four layers of the substrate, a limited number of vias are required per loop. As described with respect to Figures 6a-6e, because of the specific layers each loop is formed or provided on, each loop of a coil requires one via at an inner circumference (from the first plurality of vias 504 or second plurality of vias 506) and one via at an outer circumference (from the third plurality of vias 508 or the fourth plurality of vias 510). This provides a current sensor which can include a greater number of loops or turns, as a smaller portion of the PCB or substrate area is required to implement vias. This increases the sensitivity of the current sensor. Each loop or turn of the four measurement coils is provided with an inner circumference via being located at a unique angular position relative to the other vias of plurality of inner circumference vias. This ensures that the measurement conductors of the different turns are in different radial planes, reducing the difficulty in manufacturing the current sensor. Put another way, the loops are provided in unique radial planes.

[0141] Further each loop of each measurement coil comprises a respective one of the plurality of outer circumference vias, wherein each via of the plurality of outer circumference vias is located at a unique angular position relative to the other vias of plurality of outer circumference vias.

[0142] It should be noted that the above routing results in all loops (or turns) of each of the coils adding to the total differential voltage of the coil. In other words, all loops are constructed to behave in an additive manner with regards to sensing the current. It should be noted that other combinations of layer choices are also possible which would give the same result.

[0143] As each coil is provided across the four layers of the substrate in an alternating fashion (such that a first turn of each coil is provided on two layers, and a second turn is provided on a different two layers of the substrate) all coils occupy, on average, the same layers of the substrate. Further, the paths or routes taken by the measurement coils and return coils as they progress around the substrate are well matched, as the paths or routes of the coils are as close to each other as possible and in the same circumferential direction. This ensures that the coils pick up the same noise from outside noise sources. As such, the noise is common-mode, and can be cancelled or rejected by external signal processing circuitry, such as a differential amplifier.

[0144] The first measurement coil 204 and second measurement coil 208 are formed using vias of the first plurality of vias 504 around a single circumference. This first plurality of vias is closest to the conductor 100 or path for the conductor 522 carrying the current to be measured. As such, the inner circumference vias of both the measurement coils are an equal distance to the conductor. The same is true for the return coils, which are formed using the second plurality of vias 506, around a single circumference. Further, arranging the vias around a single circumference minimises the electrostatic coupling from outside noise sources.

[0145] Four- Laver Four Turn Current Sensor

[0146] The current sensor 500 described with respect to Figures 5a-7 includes measurement coils and return coils provided over four layers of a substrate, with a pattern that repeats every eight turns and each coil including turns on alternating pairs of layers. This provides a good electrostatic coupling performance. Another implementation is shown in Figures 8a-10, in which the current sensor is provided over four layers of a substrate, with a pattern that repeats every four turns or loops. Each coil is provided on, or includes turns on, only two layers of the substrate.

[0147] The current sensor may be implemented on a substrate comprising four layers, with four measurement coils arranged to progress at least partially around a path for a conductor through the substrate. Each measurement coil is provided on two of the four layers of the substrate. Provided on two of the four layers may mean that the majority of the conductors or conductive traces that the measurement coil comprises are located on two of the four layers of the substrate. Put another way, the measurement coil may comprise a plurality of loops, and those loops enclose an area between two of the four layers of the substrate.

[0148] A first measurement coil is provided on two of the four layers. A second measurement coil is provided on two of the four layers. A first return coil is provided on two of the four layers, with the first return coil provided on a different two layers to the two layers that the first measurement coil is provided on. A second return coil is provided on two of the four layers, with the second return coil provided on a different two layers to the two layers that the second measurement coil is provided on.

[0149] Providing the measurement coils across the four layers improves the matching of coupling of external fields into the four measurement coils. Whilst the matching is slightly lower than where each measurement coil is implemented across all four layers, the matching is still acceptable.

[0150] Further, this results in a pattern that may be repeated every four loops (or an integer multiple of four loops) of the coil, rather than every eight turns - this allows a smaller number of total loops to be provided for the current sensor, as a multiple of four total loops rather than a multiple of eight total loops is required. This is particularly advantageous in space-limited situations.

[0151] Figure 8a shows a printed circuit board, PCB, implementation 800 of the current sensor 200 shown in Figures 2a-2c, with the current sensor measurement coils implemented across four layers of the PCB. The current sensor 800 comprises a substrate 802 comprising four layers.

[0152] The current sensor 800 includes a first measurement coil 204, a first return coil 206, a second current measurement coil 208 and a second return coil 210.

[0153] The substrate 802 comprises a first plurality of vias 804 arranged around an inner circumference of the first measurement coil 204 and the second measurement coil 208. The substrate comprises a second plurality of vias 806 arranged around an inner circumference of the first return coil 206 and the second return coil 210. The first plurality of vias 804 is shown arranged around a different circumference to the second plurality of vias 806, such that the first and second plurality of vias are staggered or arranged around concentric circumferences or circles. Alternatively, the first plurality of vias 804 and the second plurality of vias 806 be arranged around the same circumference.

[0154] The substrate 302 further comprises a third plurality of vias 808 arranged around an outer circumference of the first measurement coil 204 and the second measurement coil 206. The substrate comprises a fourth plurality of vias 810 arranged around an outer circumference of the first return coil 206 and the second return coil 210. The third plurality of vias 808 and the fourth plurality of vias 810 are shown in Figure 8a as being arranged around the same circumference. However, alternatively, the third plurality of vias 808 and the fourth plurality of vias 810 may be arranged around different circumferences, such that the third and fourth plurality of vias are staggered or arranged around concentric circumferences or circles.

[0155] The current sensor 800 includes a conductor 100 for carrying a current to be measured by the first current measurement coil 204 and the second current measurement coil 206. The conductor 100 is implemented along a path 822 of the substrate 802. The path 822 may be an aperture for receiving the conductor 100. Alternatively, the conductor 100 may be a conductive trace running through the substrate, with no aperture present. The conductor 100 or path for the conductor 822 is located centrally, such that the first measurement coil 204, second measurement coil 208, first return coil 206 and second return coil 210 are formed as circles around or centred on the conductor 100. The conductor 100 may be any conductor suitable for carrying a current to be measured by the current sensor.

[0156] The first current measurement coil 204, the second current measurement coil 208, the first return coil 206 and the second return coil 210 are implemented across the four layers of the substrate, comprising conductors or conductive traces on the different layers of the substrate. A legend is provided on the figure, wherein the conductors on different layers of the substrate 802 are represented using different line formats.

[0157] The first plurality of vias 804 and the third plurality of vias 808 are used to couple conductors or conductive traces of the first measurement coil 204 and the second measurement coil 208. The second plurality of vias 806 and the fourth plurality of vias 810 are used to couple conductor or conductive traces of the first return coil 206 and the second return coil 210. The vias allows loops or turns to be formed for the measurement and return coils which span multiple layers of the substrate. The first plurality of vias 504 and the third plurality of vias 508 form the turns or loops of the first measurement coil 204 and the second measurement coil 208. The second plurality of vias 506 and the fourth plurality of vias 510 form the turns or loops of the first return coil 206 and the second return coil 210.

[0158] Each of the coils include conductors on two layers of the substrate. Each layer of the substrate 802 comprises a plurality of measurement conductors. A first plurality 814 of measurement conductors are located on a first layer of the substrate 802. A second plurality 816 of measurement conductors are located on a second layer of the substrate 802. A third plurality 818 of measurement conductors are located on a third layer of the substrate 802. A fourth plurality 820 of measurement conductors are located on a fourth layer of the substrate 802. The measurement conductors are located in radial planes from the conductor 100 or path for the conductor.

[0159] The third plurality of measurement conductors 818 and the fourth plurality of measurement conductors 820 cannot be seen in Figure 8a, as the first plurality of measurement conductors 814 and the second plurality of measurement conductors 816 are located in the same plane as the third plurality of measurement conductors 818 and the fourth plurality of measurement conductors 820.

[0160] The measurement coils are made up of measurement conductors on two of the four layers of the substrate.

[0161] Figure 8d shows a three-dimensional side view of the current sensor 800, in which the third plurality of measurement conductors 818 and the fourth plurality of measurement conductors 820 can be seen.

[0162] The substrate 802 further comprises a plurality of circumferential progression conductors 812. The circumferential progression conductors are arranged to provide circumferential progression for the measurement coils and for the return coils around the conductor 100 or path for the conductor 822. The circumferential progression conductors may be referred to as an advancement region of the substrate 802, as they allow the coils to progress or advance around the substrate 802 and around the conductor 100 or path for the conductor 822.

[0163] Figure 8b shows the current sensor 800 of Figure 8a, with only the first measurement coil 204 and the first return coil 206 present.

[0164] Figure 8c shows the current sensor 800 of Figure 8a, with only the second measurement coil 208 and the second return coil 210 present. Figures 9a-9e show a simplified subsection of the conductive traces and vias of the measurement and return coils of Figures 8a-8d. Figure 9a has reference numerals related to parts of the first measurement coil 204. Figure 9b has reference numerals related to parts of the second measurement coil 208. Figure 9c has reference numerals related to parts of the first return coil 206. Figure 9d has reference numerals related to parts of the second return coil 210.

[0165] Considering Figure 9a, the first measurement coil 204 includes a plurality of loops or turns.

[0166] A first turn or loop of the first current measurement coil 204 comprises a circumferential progression conductor 902 on the third layer of the substrate. A first end of the circumferential progression conductor 902 is coupled to a second end of a measurement conductor 904 of the third plurality of measurement conductors 818 on the third layer of the substrate. A first end of measurement conductor 904 is coupled to a via 906 of the first plurality of vias 804. A first end of a measurement conductor 908 of the first plurality of measurement conductors 814 on the first layer of the substrate is coupled to the via 906. A second end of the measurement conductor 908 is coupled to a first end of a circumferential progression conductor 910 on the first layer of the substrate. A second end of the circumferential progression conductor 910 is coupled to a via 912 of the third plurality of vias 808. The first turn or loop begins at the outer circumference of the measurement coil, progresses on the third layer to the inner circumference of the measurement coil, switches to the first layer and then progresses to the outer circumference of the measurement coil on the first layer. In this way, a turn or loop is formed across the third and first layer of the substrate.

[0167] Put another way, a loop of the first measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductor coupled to one another by a respective via of the first plurality of vias, and the loop of the first measurement coil is coupled to a further loop of the first measurement coil by a respective via of the third plurality of vias.

[0168] The first ends of the respective conductors are closer to the inner circumference of the coil, or closer to the current carrying conductor 100 or path for the current carrying conductor 822. Whilst the vias are described as inner and outer circumferences, it is clear that the vias may be provided in a number of different shapes, with the inner vias closer to the conductor 100 or path 822, and the outer vias further from the conductor 100 or path 822.

[0169] The first measurement coil 204 includes a plurality of turns or loop. All turns or loops of the first measurement coil 204 are formed on the third and first layers of the substrate 802. As such, a second turn or loop of the first measurement coil is also formed on the first and third layers of the substrate and coupled to the first turn at via 912.

[0170] Whilst the progression of the loops of the first measurement coil 204 have been described as travelling from the left side of Figure 9a to the right side of Figure 9a, it should be appreciated that this is for ease of description only and does not specifically describe the direction of travel around the circumference from the starting point of the coil. A voltage induced in the first loop of the measurement coil by the rate of change of a current in the conductor 100 creates a cumulative voltage across the measurement coil when all the loops that are joined together are considered. The progression of the loops with respect to Figures 9a-9d have been described in a single direction, however the progression of the loops may be in a clockwise or anti-clockwise direction, as described previously. As such, loops of the different coils may progress in different or opposite directions.

[0171] Considering Figure 9b, the second measurement coil 208 includes a plurality of loops or turns.

[0172] A first turn or loop of the second current measurement coil 208 comprises a circumferential progression conductor 914 on the second layer of the substrate. A first end of the circumferential progression conductor 914 is coupled to a second end of a measurement conductor 916 of the second plurality of measurement conductors 816 on the second layer of the substrate. A first end of measurement conductor 916 is coupled to a via 918 of the first plurality of vias 804. A first end of a measurement conductor 920 of the fourth plurality of measurement conductors 820 on the fourth layer of the substrate is coupled to the via 918. A second end of the measurement conductor 920 is coupled to a first end of a circumferential progression conductor 922 on the fourth layer of the substrate. A second end of the circumferential progression conductor 922 is coupled to a via 924 of the third plurality of vias 808. The first turn or loop begins at the outer circumference of the measurement coil, progresses on the second layer to the inner circumference of the measurement coil, switches to the fourth layer and then progresses to the outer circumference of the measurement coil on the fourth layer. In this way, a turn or loop of the second measurement coil is formed across the second and fourth layers of the substrate.

[0173] Put another way, a loop of the second measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the first plurality of vias, and the loop of the second measurement coil is coupled to a further loop of the second measurement coil by a respective via of the third plurality of vias. The second measurement coil 208 includes a plurality of turns or loop. All turns or loops of the second measurement coil 208 are formed on the second and fourth layers of the substrate 802. As such, a second turn or loop of the second measurement coil is also formed on the second and fourth layers of the substrate and coupled to the first turn at via 924.

[0174] Considering Figure 9c, the first return coil 206 includes a plurality of loops or turns.

[0175] A first turn or loop of the first return coil 206 comprises a circumferential progression conductor 938 on the second layer of the substrate. A first end of the circumferential progression conductor 938 is coupled to a second end of a measurement conductor 940 of the second plurality of measurement conductors 816 on the second layer of the substrate. A first end of measurement conductor 940 is coupled to a via 942 of the second plurality of vias 806. A first end of a measurement conductor 944 of the fourth plurality of measurement conductors 820 on the fourth layer of the substrate is coupled to the via 942. A second end of the measurement conductor 944 is coupled to a first end of a circumferential progression conductor 946 on the fourth layer of the substrate. A second end of the circumferential progression conductor 946 is coupled to a via 948 of the fourth plurality of vias 810. The first turn or loop begins at the outer circumference of the return coil, progresses on the second layer to the inner circumference of the return coil, switches to the fourth layer and then progresses to the outer circumference of the return coil on the fourth layer. In this way, a turn or loop of the first return coil is formed across the second and fourth layers of the substrate.

[0176] Put another way, a loop of the firs return coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the second plurality of vias, and the loop of the first return coil is coupled to a further loop of the first return coil by a respective via of the fourth plurality of vias.

[0177] The first return coil 206 includes a plurality of turns or loop. All turns or loops of the first return coil 206 are formed on the second and fourth layers of the substrate 802. As such, a second turn or loop of the first return coil is also formed on the second and fourth layers of the substrate and coupled to the first turn at via 948.

[0178] Considering Figure 9d, the second return coil 210 includes a plurality of loops or turns.

[0179] A first turn or loop of the second return measurement coil 210 comprises a circumferential progression conductor 926 on the third layer of the substrate. A first end of the circumferential progression conductor 926 is coupled to a second end of a measurement conductor 928 of the third plurality of measurement conductors 818 on the third layer of the substrate. A first end of measurement conductor 928 is coupled to a via 930 of the second plurality of vias 806. A first end of a measurement conductor 932 of the first plurality of measurement conductors 814 on the first layer of the substrate is coupled to the via 930. A second end of the measurement conductor 932 is coupled to a first end of a circumferential progression conductor 934 on the first layer of the substrate. A second end of the circumferential progression conductor 934 is coupled to a via 936 of the fourth plurality of vias 810. The first turn or loop begins at the outer circumference of the return coil, progresses on the third layer to the inner circumference of the return coil, switches to the first layer and then progresses to the outer circumference of the return coil on the first layer. In this way, a turn or loop of the second return coil is formed across the third and first layers of the substrate.

[0180] Put another way, a loop of the second return coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the second plurality of vias, and the loop of the second return coil is coupled to a further loop of the second return coil by a respective via of the fourth plurality of vias.

[0181] The second return coil 210 includes a plurality of turns or loop. All turns or loops of the second return coil 210 are formed on the third and first layers of the substrate 802. As such, a second turn or loop of the second return coil is also formed on the third and first layers of the substrate and coupled to the first turn at via 936.

[0182] Figure 9a-9d show a further plurality of outer measurement conductors 950, referenced in Figure 9e. The outer measurement conductors may be coupled between respective circumferential progression conductors of the plurality of circumferential progression conductors 812 and the vias of the third plurality of vias 808 and fourth plurality of vias 810 respectively. These have not been described for simplicity. The outer measurement conductors 950 are optional, and instead the circumferential progression conductors may be directly coupled or connected to the vias of the third plurality of vias 808 and fourth plurality of vias 810. Further, the plurality of circumferential progression elements may be positioned anywhere between the first 804 / second 806 plurality of vias and the third 808 / fourth 810 plurality of vias. The circumferential progression conductors may be positioned adjacent to or directly connected to the inner circumference vias 804, 806. The circumferential progression conductors may be positioned adjacent to or directly connected to the outer circumference vias 808, 810. The circumferential progression conductors may be positioned between the inner circumference vias 804, 806 and the outer circumference vias 808, 810, with both ends of the circumferential progression conductors 812 coupled to measurement conductors which are then coupled to the vias.

[0183] As such, the measurement conductors of the first-fourth plurality of measurement conductors may actually be coupled to outer ends or the second ends of the plurality of circumferential progression conductors 812.

[0184] Figure 10 shows a simplified subsection of the conductive traces and vias of the measurement and return coils of Figures 8a-8d. Figure 10 also shows a wider view of the simplified traces of Figures 9a-9e.

[0185] As shown in Figure 10, the first measurement coil 204 comprises a first turn 1002. Adjacent to the first turn 1002 of the first measurement coil is a first turn 1004 of the second return coil 210, a first turn 1006 of the second measurement coil 208, a first turn 1008 of the first return coil 206.

[0186] The first measurement coil 204, the first return coil 206, the second measurement coil 208 and the second return coil 210 are provided on the substrate in a repeating pattern which repeats every four adjacent turns or loops. As such, the section 1018 of the current sensor comprises four turns (one turn of each of the measurement and return coils). This section 1018 is repeated throughout the current sensor. Any other repeating order of the measurement coil loops or turns may be provided on the substrate - for example, the four loops may be provided in a different order on the substrate.

[0187] Figures 9a-9e and Figure 10 show each measurement coil provided across two layers of the substrate. It should be understood that the specific layers that the measurement coils are provided across are one example of the layers that the measurement coils may be provided across.

[0188] More generally, the first measurement coil may be provided on a different two layers of the substrate to that of the second measurement coil. Alternatively, the first measurement coil and the second measurement coil are provided on the same two layers of the substrate.

[0189] As shown in Figures 9a-9e and Figure 10, the first measurement coil is provided on the first layer and the third layer of the substrate, the second measurement coil is provided on the second layer and the fourth layer of the substrate, the first return coil is provided on the second layer and the fourth layer of the substrate, and the second return coil is provided on the first layer and the third layer of the substrate. Put another way, the current sensor 500 may be considered to comprise four pluralities of loops. The first measurement coil comprises a first plurality of loops formed on the first and third layers of the substrate. The second measurement coil comprises a second plurality of loops formed on the second and fourth layers of the substrate. The first return coil comprises a third plurality of loops formed on the second and fourth layers of the substrate. The second return coil comprises a fourth plurality of loops formed on the first and third layers of the substrate. Each loop of the measurement coils comprises conductive traces providing radial advancement between an inner circumference and an outer circumference of the measurement coils, and conductive traces providing circumferential advancement around the path.

[0190] The pluralities of loops are ordered, such that a turn of the first plurality of loops is followed by or adjacent to in a circumferential direction to a turn of the fourth plurality of loops. This is then followed by a turn of the second plurality of loops and a turn of the third plurality of loops.

[0191] As such, the first turn 1008 of the first return coil 206 is directly adjacent to a second turn 1010 of the first measurement coil in a circumferential direction around the substrate, which is adjacent to or followed by the following turns in a circumferential direction around the substrate: a second turn 1012 of the second return coil 210, a second turn 1014 of the second measurement coil 208 and a second turn 1016 of the first return coil 206. The turns of the respective coils are provided in this order in a circumferential direction around the coils.

[0192] By repeating the loops of the measurement coils in this fashion, with each coil provided across two layers of the substrate, a limited number of vias are required per loop. As described with respect to Figures 9a-9e, because of the specific layers each loop is formed or provided on, each loop of a coil requires one via at an inner circumference (from the first plurality of vias 504 or second plurality of vias 506) and one via at an outer circumference (from the third plurality of vias 508 or the fourth plurality of vias 510). This provides a current sensor which can include a greater number of loops or turns, as a smaller portion of the PCB or substrate area is required to implement vias.

[0193] Respective loops of the first plurality of loops, the second plurality of loops, the third plurality of loops and the fourth plurality of loops are positioned in adjacent radial planes. The radial planes are arranged to surround the path.

[0194] Put another way, the first measurement coil, the second measurement coil, the first return coil and the second return coil are arranged in a repeating interleaved pattern. The repeating interleaved pattern may repeat every four loops. It should, however, be understood that the repeating pattern may comprise more than one loop of each coil (an integer number of loops of each coil), and repeat every integer multiple of four loops.

[0195] The first measurement coil, the second measurement coil, the first return coil and the second return coil are provided on the substrate such that they form a repeating pattern in a circumferential direction around the path. The repeating pattern comprises a plurality of motifs, which are portions of the coil that are arranged in a repeating manner, wherein each motif of the repeating pattern comprises a loop of the first plurality of loops, a loop of the second plurality of loops, a loop of the third plurality of loops and a loop of the fourth plurality of loops.

[0196] It should be noted that the above routing results in all loops (or turns) of each of the coils adding to the total differential voltage of the coil. In other words, all loops are constructed to behave in an additive manner with regards to sensing the current. It should be noted that other combinations of layer choices are also possible which would give the same result.

[0197] Each coil is provided across two layers of the four layers of the substrate (such that the first measurement coil 204 and the second return coil 210 are provided on the first and third layers of the substrate, and the second measurement coil 208 and first return coil 206 are provided on the second and fourth layers of the substrate). The paths or routes taken by the measurement coils and return coils as they progress around the substrate are well matched, as the paths or routes of the coils are as close to each other as possible and in the same circumferential direction. This ensures that the coils pick up the same noise from outside noise sources. As such, the noise is common-mode, and can be cancelled or rejected simply by external signal processing circuitry, such as a differential amplifier.

[0198] Whilst Figures 9 and 10 show one layer implementation, other implementations are possible.

[0199] For example, the first measurement coil is provided on the first layer and the third layer of the substrate, the second measurement coil is provided on the first layer and the third layer of the substrate, the first return coil is provided on the second layer and the fourth layer of the substrate and the second return coil is provided on the second layer and the fourth layer of the substrate.

[0200] Alternatively, the first measurement coil is provided on the first layer and the fourth layer of the substrate, the second measurement coil is provided on the second layer and the third layer of the substrate, the first return coil is provided on the second layer and the third layer of the substrate, the second return coil is provided on the first layer and the fourth layer of the substrate. Alternatively, the first measurement coil is provided on the first layer and the fourth layer of the substrate, the second measurement coil is provided on the first layer and the fourth layer of the substrate, the first return coil is provided on the second layer and the third layer of the substrate, the second return coil is provided on the second layer and the third layer of the substrate.

[0201] The first measurement coil 204 and second measurement coil 208 are formed using vias of the first plurality of vias 804 around a single circumference. This first plurality of vias 804 is closest to the conductor 100 or path for the conductor 822 carrying the current to be measured. The inner circumference vias of both the measurement coils are an equal distance to the conductor. The same is true for the return coils, which are formed using the second plurality of vias 806, around a single circumference. Arranging the vias in this manner around a single circumference minimises electrostatic coupling.

[0202] Staggered Vias

[0203] The current sensors described with respect to Figures 5a-10 include vias at the outer circumference of the measurement coils and return coils included around a single circle or circumference. As such, the third plurality of vias 508 and fourth plurality of vias 510 of the current sensor according to Figures 5a-7 are located around a single circumference, the same distance from a centre of the path for the current carrying conductor 522 or the conductor 100. Similarly, the third plurality of vias 808 and fourth plurality of vias 810 of the current sensor according to Figures 8a-10 are located around a single circumference, the same distance from a centre of the path for the current carrying conductor 822 or the conductor 100. However, these vias may be staggered, such that alternating vias are provided on different circumferences, or at different radii or distances from the centre of the path for the conductor 522, 822.

[0204] As shown in Figure 11, first plurality of vias 1104 and the second plurality of vias 1106 are arranged such that they are different circumferences, or at different radii or distances from the centre of the path for the conductor 1122. This is the same as described for the first plurality of vias 504, 804 and second plurality of vias 506, 806 described with respect to the previous current sensors.

[0205] The outer circumference vias, including the third plurality of vias 1108 and the fourth plurality of vias 1110 are arranged in Figure 11 such that they are different circumferences, or at different radii or distances from the centre of the path for the conductor 1122. The fourth plurality of vias 1110 are provided with a shorter radii, or closer to the centre of the path for the conductor 1122 than the third plurality of vias 1108. This staggering of the outer circumference vias may also be applied to the third plurality of vias 508, 808 and fourth plurality of vias 510, 810, described with respect to the previous current sensors.

[0206] Staggering the outer circumference vias in this manner allows a greater number of turns to be provided in the current sensor. Further, it may allow multiple differential current sensors to be interleaved next to one another. Adjacent current sensors comprising four coils (two measurement, two return) can be located closer to one another due to the staggering, as the outer vias of one coil of a first current sensor may be co-located next to the outer vias of one coil of an adjacent or second current sensor. This would result in the circumferences of the current sensors partially overlapping.

[0207] Note that in both the four-layer eight turn and the four layer four turn coils, there is only 1 outer via and 1 inner via per spoke, in contrast to the coil of Figure 4 which has 3 outer vias and 1 inner via per spoke. This is an improvement that helps density of spokes and the repeatability and cost of having less vias.

[0208] Coil Hookup

[0209] It is desirable for the measurement coils to progress substantially 360 degrees around the conductor under test. To ensure that the measurement coils progress substantially around the substrate, providing improved rejection of longitudinal external fields, the start and end of each measurement coil should be located as close to one another as possible - preferably at the same, or substantially the same, angular position.

[0210] As shown in Figure 2a, the first end of first measurement coil 204 begins at terminal or node 212 and progresses or travels in an anti-clockwise direction around the path for the current carrying conductor 100 (or in an alternative implementation, in a clockwise direction), terminating at second end or node 214. First return coil 206 travels or progresses in the opposite direction to the first measurement coil 204 from node 214 to node 216, clockwise around the path for the current carrying conductor or the current carrying conductor 200. The first end 214 of the first return coil 206 is coupled to the second end 214 of the first measurement coil 204.

[0211] It is desirable for the first end 212 of the first measurement coil 204 and the second end of the first return coil 206 to be located at substantially the same position. So that both travel 360 degrees around the substrate, the node joining the coils, node 214, should also be at substantially the same position as the first end 212 of the first measurement coil 204 and the second end 216 of the first return coil 206.

[0212] As shown in Fig 9e, the outer measurement conductors 950 form additional regions of the turns or loops of the coils adjacent to the outer circumference of the coils. These outer measurement conductors 950 may therefore be considered to increase the area of the loops. In order to have good immunity from an external uniform magnetic field in the X direction of the PCB or substrate, it may be important that these outer measurement conductors 950 and the additional regions of the turns they form located at a first side of the substrate, at 12 o'clock location of the coils adjacent to the start and end points of the coils, perfectly match the turns that are opposite them at the 6 o'clock location, or 180 degrees around the substrate from the start and end points of the coils. However, since the start and end points for the coils can't occupy the same coordinate on the PCB (which would result in shorting them) they do not match. For example, with reference to Figure 12, ideally the 1st measurement coil would start and end at the same location or via 1202, and this via 1202 would be at the same radial distance as all the other outer circumference vias, including those opposite it at the other side of the substrate. Instead, the coil starts at 1202 and ends at the via labelled "Pf-Pr" or via 1210. If via 1202 was kept in its original radial location, at the same circumference of the other outer circumference vias, it will result in a shortened loop formed by the additional conductors 950. The vias 1202-1208 may therefore be move out radially to increase the loop area of this turn such that it matches the loop area created by outer measurement conductors 950 opposite it at the other side of the substrate.

[0213] The same is true of the second measurement coil 208 and the second return coil 210.

[0214] To achieve this, the node 214, which may be a via, may be offset from the circumference of the outer circumference vias. However, this results in the area enclosed by the loops at the second end 214 of the first measurement coil and first end 214 of the first return coil being different to the average area enclosed by the rest of the loops of the measurement coil. This may introduce an error into the measurement.

[0215] To counteract this, the first and last loops of the first measurement coil 204 and the first return coil 206, which may also be referred to the loops coupled to the first end and second end of the first measurement coil 204 and the first return coil 206, may be coupled to vias or nodes with different radial positions (the radial positions being distances taken from a centre of the measurement coils). The radial positions may result in the average loop area of the first and last loops being substantially the same as the average loop area of all other loops of the coils.

[0216] Alternatively, the loops 180 degrees around the coil from the first and last loop may comprise a loop area different to the average loop area, such that the average area of the loops positioned at substantially 180 degrees have the same loop area as those coupled to the turn-around via 1210. Figure 12 shows a portion of the current sensor 800 described with respect to Figures Sa- 10. The PCB layout shown in Figure 12 includes the ends of the measurement and return coils. The first end 212 of the first measurement coil 204 is coupled to a first output via 1202, this may also be referred to as a first via. The second end 216 of the first return coil is coupled to a first common mode via 1204, this may also be referred to as a second via 1204. The common mode vias may also be referred to as reference vias. The first end 218 of the second measurement coil is coupled to a second output via 1206, this may also be referred to as a third via 1206. The second end 222 of the second return coil 210 is coupled to a second common mode via 1208, this may also be referred to as a fourth via 1208.

[0217] The output and common mode vias may then be coupled to output or common mode terminals, for coupling to external signal processing circuitry.

[0218] Ideally, so as to provide improved immunity to external magnetic fields, the start point and end points of each of the four coils would be placed in the same physical location on the PCB or substrate. However, as multiple vias cannot be in the same location, this is not possible. To place the start and ends of the coils as close to one another as possible, the vias may be offset (for example, placed different circumferences, at different radial distances from a centre of the coils). This results in a shortening of the spokes, or measurement conductors, at these locations, resulting in loops or turns with a reduced area. This results in a degradation of the immunity to undesired external magnetic fields. So as to compensate for this, the four outer vias 1202-1208 which are coupled to the ends of the coils are offset in the radial direction to correct this error.

[0219] Considering only the first measurement coil 204 and the first return coil 206, the first measurement coil 204 comprises plurality of loops and the first return coil 206 comprises a plurality of loops, the plurality of loops of the first measurement coil 204 and of the first return coil 206 are formed using a plurality of measurement conductors provided on two or more layers of the substrate. The measurement conductors are coupled using a first plurality of outer circumference vias positioned at a first radial distance from a centre of the measurement coil and the return coil and a first plurality of inner circumference vias. The outer and inner circumference vias and how each loop is formed has already been described, so this will not be repeated here.

[0220] The second end of the first measurement coil 204 is coupled to the first end of the first return coil 206 at node 1210. This node 1210 may also be referred to as a "turn-around" via 1210, as it identifies where the coils switch direction or "turn-around". So as to allow the turn-around via 1210 to be positioned substantially adjacent to the first output via 1202 of the first measurement coil 204 and the first common mode via 1204 of the first return coil 206, the turn-around via 1210 may be positioned at a second radial distance from the centre of the measurement coils, the second radial distance being different to the first radial distance.

[0221] This results in the turn-around via 1210 being offset from the majority of the vias of the outer circumference vias, allowing it to be placed at the same angular position, or a similar angular position, to the first output via 1202 and the first common mode via 1204. This allows the measurement coils to progress substantially 360 degrees around the substrate. Put another way, the majority of the outer circumference vias may be located at a first radial distance from the centre of the measurement and return coils and the turn-around via may be located at a different radial distance.

[0222] Offsetting the turn-around via 1210 in the way results in the loop of the first measurement coil 204 and the loop of the second measurement coil 206, that are coupled to the turnaround via 1210 being of a different size to the remainder of the loops of the coils. This reduced area results in a mismatched coupling at the start of the coils compared to 180 degrees around the coil. This is particularly problematic where there are longitudinal external fields.

[0223] To counteract this, the size of the loops at the start of the coils may be modified or adapted to compensate for the reduced loop size. In particular, the first output via 1202 and the first common mode via 1204, which are coupled to loops of the first measurement coil 204 and the first return coil 206 may be modified to compensate.

[0224] The first output via 1202 and the first common mode via 1204 are provided at a third radial distance from the centre of the measurement coils. The third radial distance is different than the second radial distance at which the turn-around via 1210 is located.

[0225] In particular, the third radial distance may be greater than the second radial distance, and the first radial distance may be in between the second and third radial distances. In this manner, the turn-around via 1210 is provided at a smaller circumference compared to the circumference of the majority of the outer circumference vias, and the first output via 1202 and the first common mode via 1204 are provided at a greater circumference compared to the circumference of the majority of the outer circumference vias (or vice versa).

[0226] The average of the second and third radial distances may be the same as the first radial distance.

[0227] Put another way, by modifying the via position of the turn-around via 1210, the first output via 1202 and the first common mode via 1204, the size of the loops coupled to these vias is modified. The loop of the first measurement coil 204 coupled to the first output via 1202 and the loop of the first return coil 206 coupled to the first common mode via 1204 are larger than the loops of the first measurement coil 204 and the first return coil 206 that are coupled to the turn-around via 1210. The average area of these four loops is the same as the average area of the remainder of the loops of the first measurement coil 204 and the first return coil 206. This ensures that the loops located at the start and the end of the coils do not result in a mismatched noise coupling into the coils, allowing external longitudinal fields to be cancelled.

[0228] Further, to ensure that the vias are located as close to one another as possible, the first output via 1202 is located at a first angular position, the first common mode via 1204 is located at a second angular position and the turn-around via is located at a third angular position. The third angular position may be located at an angle between the angle of the first angular position and the second angular position. The third angular position is at an angle in the middle of the angle of the first angular position and the second angular position. The angular positions may be from a centre of the measurement coils. This ensures that the vias are located as close to one another as possible.

[0229] Figure 12 shows the connections for four measurement coils (two forward measurement coils and two return measurement coils), however it should be understood that it is also applicable to a system with only two measurement coils, or more than four measurement coils.

[0230] The system may also include a second measurement coil 208 and a second return coil 210. The second measurement coil 208 comprises plurality of loops and the second return coil 210 comprises a plurality of loops, the plurality of loops of the second measurement coil 208 and of the second return coil 210 are formed using a plurality of measurement conductors provided on two or more layers of the substrate. The measurement conductors are coupled using a plurality of outer circumference vias positioned at a first radial distance from a centre of the measurement coil and the return coil and a first plurality of inner circumference vias. The outer and inner circumference vias and how each loop has been coupled has already been described, so this will not be repeated here.

[0231] The second end of the second measurement coil 208 is coupled to the first end of the second return coil 210 at node 1212. This node 1212 may also be referred to as a "turnaround" via 1212, as it identifies where the coils switch direction or "turn-around". So as to allow the turn-around via 12 to be positioned substantially adjacent to the second output via 1206 of the second measurement coil 208 and the second common mode via 1208 of the second return coil 210, the turn-around via 1212 may be positioned at the second radial distance from the centre of the measurement coils, the second radial distance being different to the first radial distance. This results in the turn-around via 1212 being offset from the majority of the vias of the outer circumference vias, allowing it to be placed at the same angular position, or a similar angular position, to the second output via 1206 and the second common mode via 1208. This allows the measurement coils to progress substantially 360 degrees around the substrate. Put another way, the majority of the outer circumference vias may be located at a first radial distance from the centre of the measurement and return coils and the turnaround via may be located at a different radial distance.

[0232] The second output via 1206 and the second common mode via 1208 are provided at the third radial distance from the centre of the measurement coils. The third radial distance is different than the second radial distance at which the second turn-around via 1212 is located.

[0233] The second turn-around via 1212 is provided at a smaller circumference compared to the circumference of the majority of the outer circumference vias, and the second output via 1206 and the second common mode via 1208 are provided at a greater circumference compared to the circumference of the majority of the outer circumference vias (or vice versa).

[0234] The loop of the second measurement coil 208 coupled to the second output via 1206 and the loop of the second return coil 210 coupled to the second common mode via 1208 are larger than the loops of the second measurement coil 208 and the second return coil 210 that are coupled to the second turn-around via 1212. The average area of these four loops is the same as the average area of the remainder of the loops of the second measurement coil 208 and the second return coil 210. This ensures that the loops located at the start and the end of the coils do not result in a mismatched noise coupling into the coils, allowing external longitudinal fields to be cancelled.

[0235] Further, to ensure that the vias are located as close to one another as possible, the second output via 1206 is located at a fourth angular position, the second common mode via 1208 is located at a fifth angular position and the second turn-around via 1212 is located at a sixth angular position. The sixth angular position may be located at an angle between the angle of the fourth angular position and the fifth angular position. The sixth angular position is at an angle in the middle of the angle of the fourth angular position and the fifth angular position. The angular positions may be from a centre of the measurement coils. This ensures that the vias are located as close to one another as possible. Although it is preferable to compensate near the start and ending point of the coils, as described with respect to Figure 12, it is also possible to compensate at the opposite side of the circumference, substantially 180degrees from the start or end points of the coils.

[0236] Figure 13 shows the compensation provided 180degrees from the start or end points of the coils, opposite the start or end points of the coils. A first via 1302 of the third plurality of vias 808 is coupled to the first measurement coil 204. A second via 1304 of the third plurality of vias 808 is coupled to the second measurement coil 208. A first via 1306 of the fourth plurality of vias 810 is coupled to the first return coil 206. A second via 1308 of the fourth plurality of vias 810 is coupled to the second return coil 210. These vias provide the connection between layers at the outer circumference of the coils, as described with respect to Figures 9a-9e. The vias 1302-1308 are provided closer to the conductor 100 or path for the conductor 822 than the other vias of the third plurality of vias 808 and fourth plurality of vias 810. This results in a turn of each of the coils at the opposite side of the substrate to the starts and ends of the coils having a shorter radial length, and thus a smaller loop area.

[0237] With reference to only the first measurement coil 204 and the first return coil 206, a fourth via 1302 and a fifth via 1306 are located substantially 180° around the substrate from the turn-around via 1210, wherein the fourth via 1302 and the fifth via 1306 are provided at a fourth radial distance from the centre of the measurement coils. The fourth radial distance may be substantially the same as the second radial distance. A difference between the first and second radial distances is substantially the same as a distance between the first and fourth radial distances. The second radial distance is less than the first radial distance, and wherein the fourth radial distance is less than the first radial distance.

[0238] A loop of the first measurement coil 204 and a loop of the first return coil 206 are, respectively, coupled to the fourth via 1302 and the fifth via 1306. The fourth via 1302 and the fifth via 1306 are used to form a first shortened loop of the first measurement coil 204 and a second shortened loop of the first return coil 206.

[0239] As such, the shortened loops substantially 180 degrees around the substrate from the turnaround via 1210 are substantially the same loop area as the loops coupled to the turnaround via. As such, the noise coupled into these loops should be substantially the same (and of an opposite sign), providing easy cancellation of the noise.

[0240] With reference to the second measurement coil 208 and the second return coil 210, a sixth via 1304 and a seventh via 1308 are located substantially 180° around the substrate from the second turn-around via 1212, wherein the sixth via 1304 and the seventh via 1308 are provided at the fourth radial distance from the centre of the measurement coils. A loop of the second measurement coil 208 and a loop of the second return coil 210 are, respectively, coupled to the sixth via 1304 and the seventh via 1308. The sixth via 1304 and the seventh via 1308 are used to form a first shortened loop of the second measurement coil 208 and a second shortened loop of the second return coil 210.

[0241] As such, the shortened loops substantially 180 degrees around the substrate rom the second turn-around via 1212 are substantially the same loop area as the loops coupled to the second turn-around via 1212. As such, the noise coupled into these loops should be substantially the same (and of an opposite sign), providing easy cancellation of the noise.

[0242] Whilst Figures 12 and 13 describe the positioning of the vias for compensation with respect to the current sensor 800, the same via positioning may also be applied to the current sensor 500 or any other current sensor comprising two or more coils.

[0243] The modification of via positioning may be described in another way. The first measurement coil 204 comprises a first plurality of loops and the first return coil 206 comprises a second plurality of loops, the first plurality of loops and the second plurality of loops are formed using a plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using a first plurality of outer circumference vias and a first plurality of inner circumference vias (as described throughout the application as filed.

[0244] The first measurement coil 204 is coupled to the first return coil 206 at a turn-around via 1210. The majority of loops of the first plurality of loops and the second plurality of loops enclose a first loop area. This loop area is determined by the positioning of the inner and outer circumference vias and by the layer on which the measurement conductors are formed. To allow the start and end of each coil to be positioned as close to one another as possible, a loop of the first plurality of loops that is coupled to the turn-around via and a loop of the second plurality of loops that is coupled to the turn-around via enclose a second loop area. The second loop area is smaller or larger than the average loop area of the remaining loops of the first plurality of loops and the second plurality of loops, allowing the loops coupled to the turn-around via to be positioned close to the loops at the other ends of the coils.

[0245] Further, a first loop of the first plurality of loops and a first loop of the second plurality of loops, which are coupled to output vias or terminals at the other end of the coils to the turn-around via 1210 may enclose a third loop area. Where the second loop area is less than the average or first loop area, the third loop area may be larger or greater than the average or first loop area. Output Coupling

[0246] Figure 14a shows the output terminals of the current sensors 500 and 800 comprising four current measurement coils. The first end 212 of the first measurement coil 204 (the first output via 1202) are coupled to a first or positive output terminal 1402. The first end 218 of the second measurement coil (the second output via 1206) are coupled to a second or negative output terminal 1404. The second end 216 of the first return coil (first common mode via 1204) are coupled to a reference terminal 1406. The second end 222 of the second return coil 210 (the second common mode via 1208) are coupled to the reference terminal 1406. Whilst each of the coils is described as being coupled to a via, it should be understood that these vias may instead be described as nodes, especially in cases where the coil is already on the correct layer for coupling to the output connection arrangement.

[0247] The first or positive output terminal 1402 may be coupled to a first input of a signal processing circuit. The second or negative output terminal 1404 may be coupled to a second input terminal of a signal processing circuit. The reference terminal 1406 may be coupled to a reference voltage or ground. In this way, the current sensor acts as a differential current sensor, supplying a differential output at the first or positive output terminal 1402 and at the second or negative output terminal 1404.

[0248] The coupling between the vias 1202, 1204, 1206 and 1208 and the output connection arrangement may introduce undesirable additional loop areas. These additional loop areas may pick up signal from external noise sources, or from the conductor under test. This may reduce the signal to noise ratio (SNR) of the current sensor by introducing errors which will not cancel either in the coils or in the common mode rejection of the signal processing circuitry. As such, it is desirable to ensure the connection between the measurement coils and the signal processing circuitry (provided by a connection arrangement on the substrate) reduces the noise pickup or cancels the noise pickup.

[0249] Connections between the first output via 1202 and the first output terminal 1402 are provided by a first conductive trace or connection conductor 1408 on the first layer of the substrate. Connections between the second output via 1206 and the second output terminal 1404 are provided by a second conductive trace or connection conductor 1410 on the first layer of the substrate. Connections between the first common mode via 1204 and the reference terminal 1406 are provided by a third conductive trace or connection conductor 1412 on the second layer of the substrate. Connections between the second common mode via 1208 and the reference terminal 1406 are provided by a fourth conductive trace or connection conductor 1414 on the second layer of the substrate. The connection conductors may comprise conductive material on the different layers of the substrate. These traces can also be seen in Figure 14b, which shows an alternative or three- dimensional view of the section of the current sensor shown in Figure 14a.

[0250] So as to reduce the external magnetic field pickup caused by the hook-up or connection arrangement to the processing circuitry, the third conductive trace 1412 is located below or in substantially the same plane or radial plane as the first conductive trace 1408 and the first output terminal 1402. For example, a majority of the first connection conductor 1408 and the third connection conductor 1412 are located in a plane that is perpendicular to a surface of the substrate. For example, a majority of the first connection conductor 1408 overlaps a majority of the third connection conductor 1412.

[0251] This may mean that a part, the majority or all of the first connection conductor 1408 is mirrored, symmetrical, overlapping, aligned, with at least part of the third connection conductor 1412. For example, the first connection conductor 1408 and the third connection conductor 1412 follow, at least partially, the same path. The path may be considered to be a path from along a substantially radial plane when looking through the substrate, or through a major surface of the substrate.

[0252] The first connection conductor 1408 and the third connection conductor 1412 have, at least partially, the same shape. The first connection conductor 1408 and the third connection conductor 1412 may be the same shape. In particular, the third connection conductor 1412 may be the same shape as both the first connection conductor and the terminal 1402.

[0253] The first connection conductor 1408 and the third connection conductor 1412 are coupled such that in use currents flow in the connection conductors in opposite directions. This results in a cancelling of the magnetic fields produced by the current in the conductors, and as such these magnetic fields do not result in induced current in the other conductor.

[0254] The third conductive trace 1412 may also have the same shape as one or both the first conductive trace 1408 and the first output terminal 1402.

[0255] Similarly, the fourth conductive trace 1414 is located below or in the same plane or radial plane as the second conductive trace 1410 and the second output terminal 1404. The fourth conductive trace 1414 may follow the same path, have the same shape etc. as the second conductive trace 1410, as described for the first conductive trace 1408 and the third conductive trace 1412.

[0256] The fourth conductive trace 1414 may also have the same shape as one or both of the second conductive trace 1410 and the second output terminal 1404. This reduces noise in the output of the current sensor, as the loop are formed by conductive traces 1408 and 1410 on the first layer is cancelled by the loop area formed by conductive traces 1412 and 1414 on layer 2.

[0257] Further, with respect to magnetic fields in a direction parallel to the PCB, the unintended loop area of the hook-up or connections to the terminals is minimised by having the connection conductors on layers one and two, with only a thin dielectric layer between them.

[0258] A distance between the first layer and second layer is smaller than a distance between the first layer and the third layer or a distance between the first layer and the fourth layer. A dielectric layer between the first layer and the second layer is smaller than a dielectric layer between the second layer and the third layer. Whilst the conductive traces and terminals have been described as being on the first and second layers of the substrate, they may alternatively be on the third and fourth layers of the PCB, which have a similarly thin dielectric distance between them.

[0259] The measurement coils described throughout the description may be implemented with a connection arrangement as shown in Figures 14a and 14b, however it should be understood that the connection arrangement may be applicable to any current sensor comprising two or more measurement coils, or one measurement coil and one return conductor. As such, only part of the connection arrangement shown in Figure 14a (such as the first connection conductor 1408 and the third connection conductor 1412 may be present in the connection arrangement when there are two coils).

[0260] The second connection conductor 1410 and the fourth connection conductor 1414 may be mirrored or symmetrical versions of the first connection conductor 1408 and the third connection conductor 1412.

[0261] Other schemes of hook-up and compensation in the common mode are possible that equalise the respective loop area but are of different shapes. In addition there could be a continuation of twisted pair from the nominal end of the coil or common mode, so as to locate processing circuits can be located elsewhere, and maybe shared with other coils.

[0262] Whilst the connection arrangements are shown as coupled to specific terminals in the arrangement of Figures 14a and 14b, it should be understood that the connection arrangement may be coupled, directly or indirectly, to any suitable circuits. For example, the first connection conductor 1408 may be coupled to a first circuit, the second connection conductor 1410 may be a coupled to a second circuit, the third connection conductor 1412 may be coupled to a third circuit and the fourth connection conductor 1414 may be coupled to a fourth circuit. The first circuit and second circuit may be output circuits, or the inputs of further processing circuity, or terminals for coupling to further circuitry. The third circuit and fourth circuit may be reference circuits, such as a reference node or terminal, where the reference may be ground or any other suitable reference.

[0263] Figures 15a and 15b show one turn or loop of a measurement or return coil according to any of the previously described current sensors. The loop shown in these figures is provided on the first and third layers of the substrate, however it could alternatively be implemented on any two layers of the substrate.

[0264] The turn or loop comprises a circumferential progression conductor 1502 on the third layer of the substrate. A first end of the circumferential progression conductor 1502 is coupled to a second end of a measurement conductor 1504 of the third plurality of measurement conductors on the third layer of the substrate. A first end of measurement conductor 1504 is coupled to a via 1506 of the first or second plurality of vias. A first end of a measurement conductor 1508 of the first plurality of measurement conductors on the first layer of the substrate is coupled to the via 1506. A second end of the measurement conductor 1508 is coupled to a first end of a circumferential progression conductor 1510 on the first layer of the substrate. A second end of the circumferential progression conductor 1510 is coupled to a via 1512 of the third or fourth plurality of vias.

[0265] Figure 16 shows a planar view or cross-sectional cut-through of the stack-up or layer-order of a substrate 1600. The current sensors described in this description are implemented across four layers of a substrate. The substrate 1600 may be used in the current measurement coils according to any of the preceding figures.

[0266] Substrate 1600 comprises a first layer 1602, a second layer 1604, a third layer 1606 and a fourth layer 1608 arranged in that order on the substrate, such that the layers 1-4 are arranged in a direction perpendicular to the surface of the substrate 1600. The first layer 1602 and the second layer 1604 are separated by a first distance 1610. The second layer 1604 and the third layer 1604 are separated by a second distance 1612. The third layer 1606 and the fourth layer 1608 are separated by a third distance 1612.

[0267] The first distance 1610 and the third distance 1614 are substantially the same distance. For example, the first distance 1610 and the third distance 1614 may be 0.1mm. Alternatively, the first distance 1610 and the third distance 1614 may be 0.2mm, 0.3mm etc. The second distance 1612 is larger than the first distance 1610 and the third distance 1614. For example, the second distance may be 1.7mm, alternatively, the second distance may be 1.5mm, 2mm or l-2mm. It is possible to implement these types of coils across 4-layers within a greater number of layers of a pcb, for example using layers 2 to 5, on a 6 layer board, and use layers 1 and 6 for either additional shielding or for the conductor carrying the current to measure, where layer 1 is connected to layer 6 through some vias that go through the central area of the inner circumference of the coil. Other stack-ups are possible.

[0268] Implementing the measurement coils of the preceding description across the layers of the substrate 1600 provides a loop area. The area of the loop may be maximised by providing each turn or loop across the first and third, second and fourth, first and fourth or second and third layers respectively. This ensures that almost the entire substrate thickness is used for the coil radial loops or turns of both the measurement coils and return coils.

[0269] Further, implementing the conductive traces of 1408-1414 across the first 1602 and second layers 1604 results in a small distance between the conductive traces equal to the first distance 1610. This minimises the loop area formed by the conductive traces, reducing coupled noise, and ensures that the magnetic fields of the traces cancel.

[0270] Various modifications whether by way of addition, deletion, or substitution of features may be made to the above described examples to provide further examples, any and all of which are intended to be encompassed by the appended aspects.

[0271] The terminology "coupled" used above encompasses both a direct electrical connection between two components, and an indirect electrical connection where the two components are electrically connected to each other via one or more intermediate components.

[0272] Aspects

[0273] Non-limiting aspects of the disclosure are set out in the following numbered clauses and aspects.

[0274] A first set of numbered aspects is provided below:

[0275] 1. A current sensor formed on a substrate, the current sensor comprising: a first measurement coil; a second measurement coil; a first return coil; and a second return coil.

[0276] 2. The current sensor according to aspect 1, wherein at least one of the following applies: a first end of the first return coil is coupled to a second end of the first measurement coil; a first end of the second return coil is coupled to a second end of the second measurement coil; and a second end of the first return coil is coupled to a second end of the second return coil.

[0277] 3. The current sensor according to aspect 2, wherein at least one of the following applies: a first end of the first measurement coil is coupled to a first output terminal; a first end of the second measurement coil is coupled to a second output terminal; and the second end of the first return coil and the second end of the second return coil are coupled to a reference terminal.

[0278] 4. The current sensor according to any preceding aspect, wherein the substrate comprises a first layer, a second layer, a third layer and a fourth layer.

[0279] 5. The current sensor according to any of aspects 1-4, wherein : the first measurement coil comprises a first plurality of loops; the second measurement coil comprises a second plurality of loops; the first return coil comprises a third plurality of loops; and the second return coil comprises a fourth plurality of loops.

[0280] 6. The current sensor according to aspects 5, wherein: the first measurement coil comprises a fifth plurality of loops; the second measurement coil comprises a sixth plurality of loops; the first return coil comprises a seventh plurality of loops; and the second return coil comprises an eighth plurality of loops.

[0281] 7. The current sensor according to aspect 6, wherein : the first plurality of loops are provided on the first and fourth layers of the substrate; and the fifth plurality of loops are provided on the second and third layers of the substrate.

[0282] 8. The current sensor according to aspect 7, wherein: the second plurality of loops are provided on the fourth and second layers of the substrate; and the sixth plurality of loops are provided on the third and first layers of the substrate.

[0283] 9. The current sensor according to any of aspect 8, wherein: the third plurality of loops are provided on the second and fourth layers of the substrate; and the seventh plurality of loops provided on the first and third layers of the substrate.

[0284] 10. The current sensor according to any of aspect 9, wherein the fourth plurality of loops are provided on the third and second layers of the substrate; and the eighth plurality of loops are provided on the fourth and first layers of the substrate.

[0285] 11. The current sensor according to aspect 10, wherein the loops of the first measurement coil, the second measurement coil, the first return coil and the second return coil are positioned in adjacent radial planes.

[0286] 12. The current sensor according to aspect 10 or 11, wherein the loops are provided on the substrate in a circumferential direction in the following order: the first plurality of loops; the fourth plurality of loops; the second plurality of loops; the third plurality of loops; the fifth plurality of loops; the eighth plurality of loops; the sixth plurality of loops; and the seventh plurality of loops.

[0287] 13. The current sensor according to any preceding aspect, wherein a loop of the first plurality of loops is adjacent in a circumferential direction of the sensor to a loop of the fourth plurality of loops, a loop of the second plurality of loops and a loop of the third plurality of loops.

[0288] 14. The current sensor according to any preceding aspect, wherein a repeating pattern formed by respective loops of the first, second, third, fourth, fifth, sixth, seventh and eighth plurality of loops is repeated every eight loops.

[0289] 15. The current sensor according to aspect 5, wherein the first plurality of loops are provided on the first layer and the third layer of the substrate.

[0290] 16. The current sensor according to aspect 15, wherein: the second plurality of loops are provided on the second layer and the fourth layer of the substrate.

[0291] 17. The current sensor according to aspect 16, wherein : the third plurality of loops are provided on the second layer and the fourth layer of the substrate.

[0292] 18. The current sensor according to any of aspects 17, wherein : the fourth plurality of loops are provided on the third layer and the first layer of the substrate.

[0293] 19. The current sensor according to aspect 18, wherein the first plurality of loops, the second plurality of loops, the third plurality of loops and the fourth plurality of loops are positioned in adjacent radial planes.

[0294] 20. The current sensor according to aspect 19, wherein the loops are provided on the substrate in a circumferential direction in the following order: the first plurality of loops; the fourth plurality of loops; the second plurality of loops; and the third plurality of loops.

[0295] 21. The current sensor according to any of aspects 18-20, wherein a loop of the first plurality of loops is adjacent in a circumferential direction of the sensor to a loop of the fourth plurality of loops, a loop of the second plurality of loops and a loop of the third plurality of loops.

[0296] 22. The current sensor according to any of aspects 18-21, wherein a repeating pattern formed by the loops of the first, second, third, and fourth plurality of loops is repeated every four loops.

[0297] 23. The current sensor according to any preceding aspect, wherein each loop of the first measurement coil and the second measurement coil comprises conductive traces providing radial advancement from a centre of the measurement coils and circumferential advancement around the circumference of the measurement coils.

[0298] 24. The current sensor according to any preceding aspect, wherein each loop of the first return coil and the second return coil comprises conductive traces providing radial advancement from a centre of the return coils and circumferential advancement around the circumference of the return coils.

[0299] 25. The current sensor according to any preceding aspect, wherein the current sensor comprises: a first plurality of measurement conductors arranged on the first layer; a second plurality of measurement conductors arranged on the second layer; a third plurality of measurement conductors arranged on the third layer; and a fourth plurality of measurement conductors arranged on the fourth layer, wherein the measurement conductors provide advancement in a radial direction from the centre of the coils. 26. The current sensor according to aspect 25, wherein the current sensor comprises: a first plurality of vias arranged around an inner circumference of the first measurement coil and the second measurement coil; a second plurality of vias arranged around an inner circumference of the first return coil and the second return coil; a third plurality of vias arranged around an outer circumference of the first measurement coil and the second measurement coil; and a fourth plurality of vias arranged around an outer circumference of the first return coil and the second return coil.

[0300] 27. The current sensor according to aspect 26, wherein the first plurality of vias and the second plurality of vias are arranged around concentric circumferences.

[0301] 28. The current sensor according to aspect 26, wherein the first plurality of vias and the second plurality of vias are staggered.

[0302] 29. The current sensor according to any of aspects 26-28, wherein the third plurality of vias and the fourth plurality of vias are arranged around the same circumference.

[0303] 30. The current sensor according to any of aspects 26-28, wherein the third plurality of vias and the fourth plurality of vias are staggered.

[0304] 31. The current sensor according to any of aspects 25-30, further comprising: a plurality of circumferential progression conductors coupled to the measurement conductors, the plurality of circumferential progression conductors arranged to provide advancement in a circumferential direction around the substrate.

[0305] 32. The current sensor according to aspect 31, wherein a respective loop of a measurement coil comprises: a first circumferential progression conductor; a first measurement conductor on the same layer of the substrate as the first circumferential progression conductor; a first via of the first plurality of vias, wherein a first end of the first measurement conductor is coupled to the first via and a second end of the first measurement conductor is coupled to a first end of the first circumferential progression conductor; a second measurement conductor, a first end of the second measurement conductor coupled to the first via; a second circumferential progression conductor formed on the same layer of the substrate as the second measurement conductor; and a first via of the third plurality of vias, wherein a second end of the second measurement conductor is coupled to a first end of the second circumferential progression conductor, and a second end of the second circumferential progression conductor is coupled to the first via of the third plurality of vias.

[0306] 33. The current sensor according to aspect 31 or 32, wherein a respective loop of a return coil comprises: a third circumferential progression conductor; a third measurement conductor on the same layer of the substrate as the third circumferential progression conductor; a first via of the second plurality of vias, wherein a first end of the third measurement conductor is coupled to the first via of the second plurality of vias and a second end of the third measurement conductor is coupled to a first end of the third circumferential progression conductor; a fourth measurement conductor, a first end of the fourth measurement conductor coupled to the first via of the second plurality of vias; a fourth circumferential progression conductor formed on the same layer of the substrate as the fourth measurement conductor; and a first via of the fourth plurality of vias, wherein a second end of the fourth measurement conductor is coupled to a first end of the fourth circumferential progression conductor, and a second end of the fourth circumferential progression conductor is coupled to the first via of the fourth plurality of vias.

[0307] 34. The current sensor according to any of aspects 25-32, an advancement region of the coils is one of: adjacent to the first plurality of vias and the second plurality of vias; adjacent to the third plurality of vias and the fourth plurality of vias; or between the first plurality of vias and the third plurality of vias.

[0308] 35. The current sensor according to any of aspects 4-34, wherein: the first end of the first measurement coil is coupled to a first output via; the first end of the second measurement coil is coupled to a second output via; the second end of the first return coil is coupled to a first common mode via; and the second end of the second return coil is coupled to a second common mode via.

[0309] 36. The current sensor according to any of aspects 24-35, wherein the first output via, the second output via, the first common mode via and the second common mode via are arranged around an outer circumference, wherein the outer circumference has a greater radius than a radius of the third plurality of vias or the fourth plurality of vias.

[0310] 37. The current sensor according to any of aspects 24-35, wherein a loop of each of the first measurement coil, the second measurement coil, the first return coil and the second return coil at an opposite side of the substrate to the first output via, the second output via, the first common mode via and the second common mode via are shorter than the average loop length of the first measurement coil, the second measurement coil, the first return coil and the second return coil.

[0311] 38. The current sensor according to aspect 36 or 37, wherein: the first output via is coupled to the first output terminal using a first conductive trace; the second output via is coupled to the second output terminal using a second conductive trace; the first common mode via is coupled to the reference terminal using a third conductive trace; the second common mode via is coupled to the reference terminal using a fourth conductive trace, and wherein the first conductive trace and the third conductive trace are located in a first plane, and wherein the second conductive trace and the fourth conductive trace are located in a second plane.

[0312] Another set of numbered aspects is provided below:

[0313] 1. A current sensor, the current sensor comprising : a substrate comprising four layers; a path for a conductor through the substrate; a first measurement coil provided on two of the four layers of the substrate and arranged to progress at least partially around the path; a second measurement coil provided on two of the four layers of the substrate and arranged to progress at least partially around the path; a third measurement coil, coupled to the first measurement coil, progressing at least partially around the path in an opposite direction to the first measurement coil, wherein the third measurement coil is provided on the other two of the four layers of the substrate to the first measurement coil; and a fourth measurement coil, coupled to the second measurement coil, progressing at least partially around the path in an opposite direction to the second measurement coil, wherein the fourth measurement coil is provided on the other two of the four layers of the substrate to the second measurement coil.

[0314] 2. The current sensor according to aspect 1, wherein: the first measurement coil is provided on a different two layers of the substrate to that of the second measurement coil.

[0315] 3. The current sensor according to aspect 1, wherein: the first measurement coil and the second measurement coil are provided on the same two layers of the substrate.

[0316] 4. The current sensor according to aspect 1, wherein: the four layers of the substrate comprise a first layer, a second layer, a third layer and a fourth layer, arranged in that order.

[0317] 5. The current sensor according to aspect 4, wherein: the first measurement coil is provided on the first layer and the third layer of the substrate; the second measurement coil is provided on the second layer and the fourth layer of the substrate; the third measurement coil is provided on the second layer and the fourth layer of the substrate; and the fourth measurement coil is provided on the first layer and the third layer of the substrate.

[0318] 6. The current sensor according to aspect 4, wherein: the first measurement coil is provided on the first layer and the third layer of the substrate; the second measurement coil is provided on the first layer and the third layer of the substrate; the third measurement coil is provided on the second layer and the fourth layer of the substrate; and the fourth measurement coil is provided on the second layer and the fourth layer of the substrate.

[0319] 7. The current sensor according to aspect 4, wherein: the first measurement coil is provided on the first layer and the fourth layer of the substrate; the second measurement coil is provided on the second layer and the third layer of the substrate; the third measurement coil is provided on the second layer and the third layer of the substrate; and the fourth measurement coil is provided on the first layer and the fourth layer of the substrate.

[0320] 8. The current sensor according to aspect 4, wherein: the first measurement coil is provided on the first layer and the fourth layer of the substrate; the second measurement coil is provided on the first layer and the fourth layer of the substrate; the third measurement coil is provided on the second layer and the third layer of the substrate; and the fourth measurement coil is provided on the second layer and the third layer of the substrate.

[0321] 9. The current sensor according to any preceding aspect, wherein: the first measurement coil comprises a first plurality of loops; the second measurement coil comprises a second plurality of loops; the third measurement coil comprises a third plurality of loops; and the fourth measurement coil comprises a fourth plurality of loops. 10. The current sensor according to aspect 9, wherein respective loops of the first plurality of loops, the second plurality of loops, the third plurality of loops and the fourth plurality of loops are positioned in adjacent radial planes.

[0322] 11. The current sensor according to aspect 10, wherein the radial planes are arranged to surround the path.

[0323] 12. The current sensor according to any of aspects 9-11, wherein the first measurement coil, the second measurement coil, the third measurement coil and the fourth measurement coil are arranged in a repeating interleaved pattern.

[0324] 13. The current sensor according to aspect 12, wherein the repeating interleaved pattern repeats every four loops.

[0325] 14. The current sensor according to any of aspects 9-11, wherein the first measurement coil, the second measurement coil, the third measurement coil and the fourth measurement coil are provided on the substrate such that they form a repeating pattern in a circumferential direction around the path.

[0326] 15. The current sensor according to any of aspects 9-14, wherein the repeating pattern comprises a plurality of motifs arranged in a repeating manner, wherein each motif of the repeating pattern comprises a loop of the first plurality of loops, a loop of the second plurality of loops, a loop of the third plurality of loops and a loop of the fourth plurality of loops.

[0327] 16. The current sensor according to any of aspects 9-15, wherein each loop of the measurement coils comprises conductive traces providing radial advancement between an inner circumference and an outer circumference of the measurement coils, and conductive traces providing circumferential advancement around the path.

[0328] 17. The current sensor according to any of aspects 9-16, wherein the current sensor comprises: a first plurality of measurement conductors provided on the first layer; a second plurality of measurement conductors provided on the second layer; a third plurality of measurement conductors provided on the third layer; and a fourth plurality of measurement conductors provided on the fourth layer, wherein the measurement conductors provide advancement in a radial direction between an inner circumference and an outer circumference of the measurement coils.

[0329] 18. The current sensor according to any of aspects 9-17, wherein the current sensor comprises: a first plurality of vias provided on the substrate and arranged around an inner circumference of the first measurement coil and the second measurement coil; a second plurality of vias provided on the substrate and arranged around an inner circumference of the third measurement coil and the fourth measurement coil; a third plurality of vias provided on the substrate and arranged around an outer circumference of the first measurement coil and the second measurement coil; and a fourth plurality of vias provided on the substrate and arranged around an outer circumference of the third measurement coil and the fourth measurement coil.

[0330] 19. The current sensor according to aspect 18, wherein a loop of the first measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductor coupled to one another by a respective via of the first plurality of vias, and the loop of the first measurement coil is coupled to a further loop of the first measurement coil by a respective via of the third plurality of vias.

[0331] 20. The current sensor according to aspect 18 or aspect 19, wherein a loop of the second measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the first plurality of vias, and the loop of the second measurement coil is coupled to a further loop of the second measurement coil by a respective via of the third plurality of vias.

[0332] 21. The current sensor according to any of aspects 18-20, wherein a loop of the third measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the second plurality of vias, and the loop of the third measurement coil is coupled to a further loop of the third measurement coil by a respective via of the fourth plurality of vias.

[0333] 22. The current sensor according to any of aspects 18-21, wherein a loop of the fourth measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the second plurality of vias, and the loop of the fourth measurement coil is coupled to a further loop of the fourth measurement coil by a respective via of the fourth plurality of vias.

[0334] 23. The current sensor according to aspect 18-22, wherein the first plurality of vias and the second plurality of vias are arranged around the same circumference.

[0335] 24. The current sensor according to aspect 18-22, wherein the first plurality of vias and the second plurality of vias are arranged around staggered circumferences.

[0336] 25. The current sensor according to any preceding aspect, wherein: the first measurement coil comprises a first end and a second end; the second measurement coil comprises a first end and a second end; the third measurement coil comprises a first end and a second end; and the fourth measurement coil comprises a first end and a second end; wherein the second end of the first measurement coil is coupled to the first end of the third measurement coil; wherein the second end of the second measurement coil is coupled to the first end of the fourth measurement coil.

[0337] 26. The current sensor according to aspect 25, wherein the second end of the third measurement coil is coupled to the second end of the fourth measurement coil.

[0338] 27. The current sensor according to aspect 25 or 26, wherein at least one of the following applies: the first end of the first measurement coil is coupled to a first output terminal; the first end of the second measurement coil is coupled to a second output terminal; and the second end of the third measurement coil and the second end of the fourth measurement coil are coupled to a reference terminal.

[0339] 28. The current sensor according to any preceding aspect, wherein the path for the conductor passes through the measurement coils.

[0340] 29. The current sensor according to aspect 28, wherein the conductor is for carrying a current, and wherein the current sensor is for measuring the current carried by the conductor.

[0341] 30. A current sensor, the current sensor comprising : a substrate comprising four layers; a path for a conductor through the substrate; a first measurement coil provided on two of the four layers of the substrate and arranged to progress at least partially around the path; a second measurement coil provided on two of the four layers of the substrate and arranged to progress at least partially around the path; a third measurement coil, coupled to the first measurement coil, provided on two of the four layers of the substrate and arranged to progress at least partially around the path; and a fourth measurement coil, coupled to the second measurement coil, provided on two of the four layers of the substrate and arranged to progress at least partially around the path.

[0342] 31. A current sensor, the current sensor comprising : a substrate comprising four layers; a path for a conductor through the substrate; a first measurement coil provided on two of the four layers of the substrate; a second measurement coil provided on two of the four layers of the substrate; a third measurement coil, coupled to the first measurement coil, provided on two of the four layers of the substrate; and a fourth measurement coil, coupled to the second measurement coil, provided on two of the four layers of the substrate, wherein the first measurement coil, the second measurement coil, the third measurement coil and the fourth measurement coil are provided on the substrate such that they form a repeating pattern in a circumferential direction around the path.

[0343] Another set of numbered aspects is provided below:

[0344] 1. A current sensor, the current sensor comprising : a substrate comprising four layers, the substrate comprising a plurality of measurement conductors provided on the four layers of the substrate, a plurality of inner circumference vias and a plurality of outer circumference vias, arranged so as to form: a first measurement coil comprising measurement conductors on each of the four layers; a second measurement coil comprising measurement conductors on each of the four layers; a third measurement coil comprising measurement conductors on each of the four layers; a fourth measurement coil comprising measurement conductors on each of the four layers; wherein each loop of each measurement coil comprises a respective one of the plurality of inner circumference vias, and wherein each via of the plurality of inner circumference vias is located at a unique angular position relative to the other vias of plurality of inner circumference vias.

[0345] 2. The current sensor according to aspect 1, wherein each loop of each measurement coil comprises a respective one of the plurality of outer circumference vias, wherein each via of the plurality of outer circumference vias is located at a unique angular position relative to the other vias of plurality of outer circumference vias.

[0346] 3. The current sensor according to any preceding aspect, wherein: the first measurement coil comprises a first plurality of loops and a fifth plurality of loops; the second measurement coil comprises a second plurality of loops and a sixth plurality of loops; the third measurement coil comprises a third plurality of loops and a seventh plurality of loops; and the second return coil comprises a fourth plurality of loops and an eighth plurality of loops.

[0347] 4. The current sensor according to aspect 3, wherein : the first plurality of loops are provided on two of the four layers of the substrate, and the fifth plurality of loops are provided on the other two of the four layers of the substrate to the first plurality of loops; the second plurality of loops are provided on two of the four layers of the substrate, and the sixth plurality of loops are provided on the other two of the four layers of the substrate to the second plurality of loops; the third plurality of loops are provided on two of the four layers of the substrate, and the seventh plurality of loops are provided on the other two of the four layers of the substrate to the third plurality of loops; the fourth plurality of loops are provided on two of the four layers of the substrate, and the eighth plurality of loops are provided on the other two of the four layers of the substrate to the fourth plurality of loops.

[0348] 5. The current sensor according to aspect 3 or aspect 4, wherein : the first plurality of loops are provided on the first and fourth layers of the substrate; and the fifth plurality of loops are provided on the second and third layers of the substrate.

[0349] 6. The current sensor according to any of aspects 3-5, wherein : the second plurality of loops are provided on the fourth and second layers of the substrate; and the sixth plurality of loops are provided on the third and first layers of the substrate.

[0350] 7. The current sensor according to any of aspects 3-6, wherein : the third plurality of loops are provided on the second and fourth layers of the substrate; and the seventh plurality of loops provided on the first and third layers of the substrate.

[0351] 8. The current sensor according to any of aspects 3-7, wherein : the fourth plurality of loops are provided on the third and second layers of the substrate; and the eighth plurality of loops are provided on the fourth and first layers of the substrate.

[0352] 9. The current sensor according to aspect 3, wherein respective loops of the first plurality of loops, the second plurality of loops, the third plurality of loops, the fourth plurality of loops, the fifth plurality of loops, the sixth plurality of loops, the seventh plurality of loops and the eighth plurality of loops are positioned in adjacent radial planes

[0353] 10. The current sensor according to aspect 9, wherein the radial planes progress in a radial direction between the plurality of inner circumference vias and the plurality of outer circumference vias.

[0354] 11. The current sensor according to aspect 9 or aspect 10, wherein the radial planes are arranged to surround the path.

[0355] 12. The current sensor according to any of aspects 9-11, wherein the first measurement coil, the second measurement coil, the third measurement coil and the fourth measurement coil are arranged in a repeating interleaved pattern 13. The current sensor according to aspect 12, wherein the repeating interleaved pattern repeats every eight loops.

[0356] 14. The current sensor according to aspect 13, wherein an eight loop repeating portion of the repeating interleaved pattern comprises one loop of each of the plurality of loops.

[0357] 15. The current sensor according to any of aspects 9-11, wherein the first measurement coil, the second measurement coil, the third measurement coil and the fourth measurement coil are provided on the substrate such that they form a repeating pattern in a circumferential direction around the path.

[0358] 16. The current sensor according to any of aspects 9-15, wherein the repeating pattern comprises a plurality of motifs arranged in a repeating manner, wherein each motif of the repeating pattern comprises a loop of the first plurality of loops, a loop of the second plurality of loops, a loop of the third plurality of loops, a loop of the fourth plurality of loops, a loop of the fifth plurality of loops, a loop of the sixth plurality of loops, a loop of the seventh plurality of loops and a loop of the eighth plurality of loops.

[0359] 17. The current sensor according to any of aspects 3-16, wherein the loops of the measurement coils are provided on the substrate in a repeating pattern in the following order: a loop of the first plurality of loops; a loop of the fourth plurality of loops; a loop of the second plurality of loops; a loop of the third plurality of loops; a loop of the fifth plurality of loops; a loop of the eighth plurality of loops; a loop of the sixth plurality of loops; and a loop of the seventh plurality of loops.

[0360] 18. The current sensor according to any of aspects 3-16, wherein the loops of the measurement coils are provided on the substrate in a repeating pattern in the following order: a plurality of loops of the first plurality of loops; a plurality of loops of the fourth plurality of loops; a plurality of loops of the second plurality of loops; a plurality of loops of the third plurality of loops; a plurality of loops of the fifth plurality of loops; a plurality of loops of the eighth plurality of loops; a plurality of loops of the sixth plurality of loops; and a plurality of loops of the seventh plurality of loops.

[0361] 19. The current sensor according to any preceding aspect, wherein the current sensor comprises: a first plurality of measurement conductors provided on the first layer; a second plurality of measurement conductors provided on the second layer; a third plurality of measurement conductors provided on the third layer; and a fourth plurality of measurement conductors provided on the fourth layer, wherein the measurement conductors provide advancement in a radial direction between an inner circumference and an outer circumference of the measurement coils.

[0362] 20. The current sensor according to aspect 13: wherein the plurality of inner circumference vias comprises a first plurality of vias arranged around an inner circumference of the first measurement coil and the second measurement coil; wherein the plurality of inner circumference vias comprises a second plurality of vias arranged around an inner circumference of the third measurement coil and the fourth measurement coil; wherein the plurality of outer circumference vias comprises a third plurality of vias arranged around an outer circumference of the first measurement coil and the second measurement coil; and wherein the plurality of outer circumference vias comprises a fourth plurality of vias arranged around an outer circumference of the third measurement coil and the fourth measurement coil.

[0363] 21. The current sensor according to aspect 20, wherein a loop of the first measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductor coupled to one another by a respective via of the first plurality of vias, and the loop of the first measurement coil is coupled to a further loop of the first measurement coil by a respective via of the third plurality of vias.

[0364] 22. The current sensor according to aspect 20 or aspect 21, wherein a loop of the second measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the first plurality of vias, and the loop of the second measurement coil is coupled to a further loop of the second measurement coil by a respective via of the third plurality of vias.

[0365] 23. The current sensor according to any of aspects 20-22, wherein a loop of the third measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the second plurality of vias, and the loop of the third measurement coil is coupled to a further loop of the third measurement coil by a respective via of the fourth plurality of vias.

[0366] 24. The current sensor according to any of aspects 20-23, wherein a loop of the fourth measurement coil is formed of a measurement conductor on one of the four layers of the substrate and a measurement conductor on another of the four layers of the substrate, the measurement conductors coupled to one another by a respective via of the second plurality of vias, and the loop of the fourth measurement coil is coupled to a further loop of the fourth measurement coil by a respective via of the fourth plurality of vias.

[0367] 25. The current sensor according to aspect 20-24, wherein the first plurality of vias and the second plurality of vias are arranged around the same circumference.

[0368] 26. The current sensor according to aspect 20-24, wherein the first plurality of vias and the second plurality of vias are arranged around staggered circumferences.

[0369] 27. The current sensor according to any preceding aspect, wherein: the first measurement coil comprises a first end and a second end; the second measurement coil comprises a first end and a second end; the third measurement coil comprises a first end and a second end; the fourth measurement coil comprises a first end and a second end; wherein the second end of the first measurement coil is coupled to the first end of the third measurement coil; wherein the second end of the second measurement coil is coupled to the first end of the fourth measurement coil.

[0370] 28. The current sensor according to aspect 27, wherein the second end of the third measurement coil is coupled to the second end of the fourth measurement coil.

[0371] 29. The current sensor according to aspect 27 or 28, wherein at least one of the following applies: the first end of the first measurement coil is coupled to a first output terminal; the first end of the second measurement coil is coupled to a second output terminal; and the second end of the third measurement coil and the second end of the fourth measurement coil are coupled to a reference terminal.

[0372] 30. The current sensor according to any preceding aspect, wherein the current sensor further comprises a path for a conductor through the substrate, the path passing through the measurement coils.

[0373] 31. The current sensor according to aspect 30, wherein the path for the conductor passes through the measurement coils.

[0374] 32. The current sensor according to aspect 31, wherein the conductor is for carrying a current, and wherein the current sensor is for measuring the current carried by the conductor.

[0375] 33. The current sensor according to any preceding aspect, wherein the first measurement coil, second measurement coil, third measurement coil and fourth measurement coil are arranged to progress at least partially around the path.

[0376] 34. A current sensor, the current sensor comprising : a substrate comprising four layers; a first measurement coil provided on the four layers of the substrate; a second measurement coil provided on the four layers of the substrate; a third measurement coil provided on the four layers of the substrate; a fourth measurement coil provided on the four layers of the substrate; wherein a majority of a respective loop of each measurement coil is located at a unique angular position relative to a majority of each loop of the loops of the first measurement coil, the second measurement coil, the third measurement coil and the fourth measurement coil.

[0377] 35. A current sensor, the current sensor comprising : a substrate comprising four layers; a first measurement coil provided on the four layers of the substrate; a second measurement coil provided on the four layers of the substrate; a third measurement coil provided on the four layers of the substrate; a fourth measurement coil provided on the four layers of the substrate, wherein the first measurement coil, the second measurement coil, the third measurement coil and the fourth measurement coil are provided on the substrate such that they form a repeating pattern in a circumferential direction around the path.

[0378] Another set of numbered aspects is provided below:

[0379] 1. A current sensor, the current sensor comprising : a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path; a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path; wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops, the first plurality of loops and the second plurality of loops being formed using a plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using a first plurality of outer circumference vias positioned at a first radial distance from a centre of the measurement coils and a first plurality of inner circumference vias; wherein the first measurement coil is coupled to the second measurement coil at a turn-around via, the turn-around via being positioned at a second radial distance from the centre of the measurement coils, the second radial distance being different to the first radial distance.

[0380] 2. The current sensor according to aspect 1, wherein the first measurement coil is coupled to a first via and the second measurement coil is coupled to a second via, wherein the first via and the second via are provided at a third radial distance from the centre of the measurement coils.

[0381] 3. The current sensor according to aspect 2, wherein the first via is located at a first angular position, the second via is located at a second angular position and the turn-around via is located at a third angular position.

[0382] 4. The current sensor according to aspect 3, wherein the third angular position is at an angle between the angle of the first angular position and the second angular position.

[0383] 5. The current sensor according to aspect 3, wherein the third angular position is at an angle in the middle of the angle of the first angular position and the second angular position.

[0384] 6. The current sensor according to aspect 1, wherein the first measurement coil is coupled to a first node and the second measurement coil is coupled to a second node, wherein the first node and the second node are provided at a third radial distance from the centre of the measurement coils.

[0385] 7. The current sensor according to any of aspects 2-6, wherein a difference between the first and second radial distances is substantially the same as a distance between the first and third radial distances.

[0386] 8. The current sensor according to any of aspects 2-7, wherein the second radial distance is less than the first radial distance, and wherein the first radial distance is less than the third radial distance.

[0387] 9. The current sensor according to any of aspects 2-7, wherein the third radial distance is less than the first radial distance, and wherein the first radial distance is less than second radial distance.

[0388] 10. The current sensor according to any preceding aspect, wherein the first measurement coil comprises a first end and a second end, and the second measurement coil comprises a first end and around a second end.

[0389] 11. The current sensor according to aspect 10, wherein : the first end of the first measurement coil is coupled to the first via; the second end of the first measurement coil is coupled to the first end of the second measurement coil at the turn-around via; and the second end of the second measurement coil is coupled to the second via.

[0390] 12 The current sensor according to any preceding aspect, wherein the first via is coupled to a first terminal and the second via is coupled to a second terminal.

[0391] 13. The current sensor according to aspect 1, wherein a fourth via and a fifth via are located substantially 180° around the substrate from the turn-around via, wherein the fourth via and the fifth via are provided at a fourth radial distance from the centre of the measurement coils.

[0392] 14. The current sensor according to aspect 13, wherein a difference between the first and second radial distances is substantially the same as a distance between the first and fourth radial distances. 15. The current sensor according to any of aspects 13 or 14, wherein the second radial distance is less than the first radial distance, and wherein the first radial distance is less than the fourth radial distance.

[0393] 16. The current sensor according to any of aspects 13-15, wherein a loop of the first measurement coil and a loop of the second measurement are, respectively, coupled to the fourth via and the fifth via.

[0394] 17. The current sensor according to any of aspect 13-15, wherein the fourth via and the fifth are used to form a first shortened loop of the first measurement coil and a second shortened loop of the second measurement coil.

[0395] 18. The current sensor according to aspect 17, the first shortened loop and the second shortened loop are formed using respective measurement conductors of the plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using the fourth and fifth vias respectively and vias of the first plurality of inner circumference vias.

[0396] 19. A current sensor, the current sensor comprising : a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path; and a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path; wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops, the first plurality of loops and the second plurality of loops being formed using a plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using a first plurality of outer circumference vias and a first plurality of inner circumference vias; wherein the first measurement coil is coupled to the second measurement coil at a turn-around via; wherein a majority of loops of the first plurality of loops and the second plurality of loops enclose a first loop area; wherein a loop of the first plurality of loops that is coupled to the turn-around via and a loop of the second plurality of loops that is coupled to the turn-around via enclose a second loop area.

[0397] 20. The current sensor according to aspect 19, wherein a first loop of the first plurality of loops and a first loop of the second plurality of loops enclose a third loop area.

[0398] 21. The current sensor according to aspect 20, wherein the average of the second loop area and the third loop area is the same as the first loop area.

[0399] 22. A current sensor, the current sensor comprising : a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path, the first measurement coil comprising a first end, a second end and a first plurality of loops; and a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path, the second measurement coil comprising a first end, a second end and a second plurality of loops; wherein the first end of the first measurement coil is coupled to a first terminal, the second end of the first measurement coil is coupled to the first end of the second measurement coil, and the second end of the second measurement coil is coupled to a second terminal, wherein a majority of the plurality of loops of the first measurement coil and the second measurement coil enclose a first loop area, wherein a loop of the first plurality of loops at the second end of the first measurement coil and a loop of the second plurality of loops at the first end of the second measurement coil each enclose a second loop area, wherein a loop of the first plurality of loops coil at the first end of the first measurement coil and a loop of the second plurality of loops at the second end of the second measurement coil each enclose a third loop area, wherein the average of the second loop area and the third loop area is the same as the first loop area.

[0400] A set of numbered aspects is provided below:

[0401] 1. A current sensor, the current sensor comprising : a substrate comprising a first layer and a second layer; a first measurement coil provided on the substrate, the first measurement coil comprising a first end; a second measurement coil provided on the substrate, the second measurement coil comprising a first end; and a connection arrangement, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate, wherein the first end of the first measurement coil is for coupling to a first circuit via the first connection conductor; and a second connection conductor provided on the second layer of the substrate, wherein the first end of the second measurement coil is for coupling to a second circuit via the second connection conductor, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate. 2. The current sensor according to aspect 1, wherein the first connection conductor and the second connection conductor follow, at least partially, the same path.

[0402] 3. The current sensor according to aspect 1 or 2, wherein the first connection conductor and the second connection conductor have, at least partially, the same shape.

[0403] 4. The current sensor according to any preceding aspect, wherein the first connection conductor and the second connection conductor are the same shape.

[0404] 5. The current sensor according to any preceding aspect, wherein the first connection conductor and the second connection conductor are coupled such that in use currents flow in the connection conductors in opposite directions.

[0405] 6. The current sensor according to any preceding aspect, wherein the first circuit comprises a measurement circuit.

[0406] 7. The current sensor according to any preceding aspect, wherein the second circuit comprises a reference circuit.

[0407] 8. The current sensor according to any preceding aspect, wherein the substrate further comprises a third layer and a fourth layer, and wherein the first layer, second layer, third layer and fourth layer are provided, in that order, through the substrate.

[0408] 9. The current sensor according to aspect 8, wherein a distance between the first layer and second layer is smaller than a distance between the first layer and the third layer or a distance between the first layer and the fourth layer.

[0409] 10. The current sensor according to aspect 8 or aspect 9, wherein a dielectric layer between the first layer and the second layer is smaller than a dielectric layer between the second layer and the third layer.

[0410] 11. The current sensor according to any of aspects 8-10, wherein the first measurement coil is provided across two or more of the four layers of the substrate and the second measurement coil is provided across two or more of the four layers of the substrate.

[0411] 12. The current sensor according to any preceding aspect, the current sensor further comprising: a third measurement coil provided on the substrate, the third measurement coil comprising a first end; a fourth measurement coil provided on the substrate, the fourth measurement coil comprising a first end.

[0412] 13. The current sensor according to aspect 12, wherein the connection arrangement further comprises: a third connection conductor provided on the first layer of the substrate, wherein the first end of the third measurement coil is for coupling to a third circuit via the third connection conductor; and a fourth connection conductor provided on the second layer of the substrate, wherein the first end of the fourth measurement coil is for coupling to a fourth circuit the fourth connection conductor, wherein the third connection conductor on the first layer is substantially aligned with the fourth connection conductor in a plane that is perpendicular to a surface of the substrate.

[0413] 14. The current sensor according to aspect 13, wherein the third connection conductor and fourth connection conductor are mirrored versions of the first connection conductor and the second connection conductor.

[0414] 15. The current sensor according to aspect 13 or 14, wherein the first measurement coil is coupled to the second measurement coil and the third measurement coil is coupled to the fourth measurement coil.

[0415] 16. The current sensor according to any of aspects 13-15, wherein the current sensor comprises a path through the substrate, and wherein the first measurement coil and the third measurement coil surround the path in a first circumferential direction and the second measurement coil and the fourth measurement coil surround the path in a second circumferential direction opposite to the first circumferential direction.

[0416] 17. The current sensor according to any of aspects 13-16, wherein the third circuit is the same as the first circuit and the fourth circuit is the same as the second circuit.

[0417] 18. A connection arrangement for a printed circuit board, PCB, implemented current sensor, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate wherein the first connection conductor is for coupling the PCB implemented current sensor to a first circuit; and a second connection conductor provided on the second layer of the substrate, wherein the second connection conductor is for coupling the PCB implemented current sensor to a second circuit, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor in a plane that is perpendicular to a surface of the substrate.

[0418] 19. The connection arrangement according to aspect 18, wherein the first connection conductor is for coupling to a first measurement coil of the PCB implemented current sensor and the second connection conductor is for coupling to a second measurement coil of the PCB implemented current sensor.

[0419] 20. A current sensor, the current sensor comprising : a substrate comprising a first layer and a second layer; a first measurement coil provided on the substrate, the first measurement coil comprising a first end; a second measurement coil provided on the substrate, the second measurement coil comprising a first end; a third measurement coil provided on the substrate, the third measurement coil comprising a first end; a fourth measurement coil provided on the substrate, the fourth measurement coil comprising a first end; a connection arrangement, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate, wherein the first end of the first measurement coil is for coupling to a first circuit via the first connection conductor; and a second connection conductor provided on the second layer of the substrate, wherein the first end of the second measurement coil is for coupling to a second circuit via the second connection conductor, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate; a third connection conductor provided on the first layer of the substrate, wherein the first end of the third measurement coil is for coupling to the first circuit via the third connection conductor; and a fourth connection conductor provided on the second layer of the substrate, wherein the first end of the fourth measurement coil is for coupling to the second circuit via the fourth connection conductor, wherein the third connection conductor on the first layer is substantially aligned with the fourth connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate.

[0420] 21. The current sensor according to aspect 20, wherein a second end of the first measurement coil is coupled to a second end of the second measurement coil and a second end of the third measurement coil is coupled to a second end of the fourth measurement coil.

[0421] 22. The current sensor according to aspect 20 or aspect 21, wherein the first and third measurement coils progress in a first circumferential direction around the substrate and the second and fourth measurement coils progress in a second circumferential direction, opposite to the first circumferential direction, around the substrate.

Claims

Claims1. A current sensor, the current sensor comprising : a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path; a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path; wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops, the first plurality of loops and the second plurality of loops being formed using a plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using a first plurality of outer circumference vias positioned at a first radial distance from a centre of the measurement coils and a first plurality of inner circumference vias; wherein the first measurement coil is coupled to the second measurement coil at a turn-around via, the turn-around via being positioned at a second radial distance from the centre of the measurement coils, the second radial distance being different to the first radial distance.

2. The current sensor according to claim 1, wherein the first measurement coil is coupled to a first via and the second measurement coil is coupled to a second via, wherein the first via and the second via are provided at a third radial distance from the centre of the measurement coils.

3. The current sensor according to claim 2, wherein the first via is located at a first angular position, the second via is located at a second angular position and the turn-around via is located at a third angular position.

4. The current sensor according to claim 3, wherein the third angular position is at an angle between the angle of the first angular position and the second angular position.

5. The current sensor according to claim 3, wherein the third angular position is at an angle in the middle of the angle of the first angular position and the second angular position.

6. The current sensor according to claim 1, wherein the first measurement coil is coupled to a first node and the second measurement coil is coupled to a second node, wherein the first node and the second node are provided at a third radial distance from the centre of the measurement coils.

7. The current sensor according to any of claims 2-6, wherein a difference between the first and second radial distances is substantially the same as a distance between the first and third radial distances.

8. The current sensor according to any of claims 2-7, wherein the second radial distance is less than the first radial distance, and wherein the first radial distance is less than the third radial distance.

9. The current sensor according to any of claims 2-7, wherein the third radial distance is less than the first radial distance, and wherein the first radial distance is less than second radial distance.

10. The current sensor according to any preceding claim, wherein the first measurement coil comprises a first end and a second end, and the second measurement coil comprises a first end and around a second end.

11. The current sensor according to claim 10, wherein: the first end of the first measurement coil is coupled to the first via; the second end of the first measurement coil is coupled to the first end of the second measurement coil at the turn-around via; and the second end of the second measurement coil is coupled to the second via.

12. The current sensor according to claim 1, wherein a fourth via and a fifth via are located substantially 180° around the substrate from the turn-around via, wherein the fourth via and the fifth via are provided at a fourth radial distance from the centre of the measurement coils.

13. The current sensor according to claim 12, wherein a difference between the first and second radial distances is substantially the same as a distance between the first and fourth radial distances.

14. The current sensor according to any of claims 12 or 13, wherein the second radial distance is less than the first radial distance, and wherein the first radial distance is less than the fourth radial distance.

15. The current sensor according to any of claims 12-14, wherein a loop of the first measurement coil and a loop of the second measurement are, respectively, coupled to the fourth via and the fifth via.

16. The current sensor according to any of claims 12-14, wherein the fourth via and the fifth via are used to form a first shortened loop of the first measurement coil and a second shortened loop of the second measurement coil.

17. The current sensor according to claim 16, the first shortened loop and the second shortened loop are formed using respective measurement conductors of the plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using the fourth and fifth vias respectively and vias of the first plurality of inner circumference vias.

18. A current sensor, the current sensor comprising : a substrate; a path for a conductor; a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path; and a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path; wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops, the first plurality of loops and the second plurality of loops being formed using a plurality of measurement conductors provided on two or more layers of the substrate, the measurement conductors coupled using a first plurality of outer circumference vias and a first plurality of inner circumference vias; wherein the first measurement coil is coupled to the second measurement coil at a turn-around via; wherein a majority of loops of the first plurality of loops and the second plurality of loops enclose a first loop area; wherein a loop of the first plurality of loops that is coupled to the turn-around via and a loop of the second plurality of loops that is coupled to the turn-around via enclose a second loop area.

19. The current sensor according to claim 18, wherein a first loop of the first plurality of loops and a first loop of the second plurality of loops enclose a third loop area, wherein the average of the second loop area and the third loop area is the same as the first loop area.

20. A current sensor, the current sensor comprising : a substrate; a path for a conductor;a first measurement coil provided on the substrate, the first measurement coil arranged to progress at least partially around the path, the first measurement coil comprising a first end, a second end and a first plurality of loops; and a second measurement coil provided on the substrate, the second measurement coil arranged to progress at least partially around the path, the second measurement coil comprising a first end, a second end and a second plurality of loops; wherein the first end of the first measurement coil is coupled to a first terminal, the second end of the first measurement coil is coupled to the first end of the second measurement coil, and the second end of the second measurement coil is coupled to a second terminal, wherein a majority of the plurality of loops of the first measurement coil and the second measurement coil enclose a first loop area, wherein a loop of the first plurality of loops at the second end of the first measurement coil and a loop of the second plurality of loops at the first end of the second measurement coil each enclose a second loop area, wherein a loop of the first plurality of loops coil at the first end of the first measurement coil and a loop of the second plurality of loops at the second end of the second measurement coil each enclose a third loop area, wherein the average of the second loop area and the third loop area is the same as the first loop area.

21. A current sensor, the current sensor comprising : a substrate comprising a first layer and a second layer; a first measurement coil provided on the substrate, the first measurement coil comprising a first end; a second measurement coil provided on the substrate, the second measurement coil comprising a first end; and a connection arrangement, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate, wherein the first end of the first measurement coil is for coupling to a first circuit via the first connection conductor; and a second connection conductor provided on the second layer of the substrate, wherein the first end of the second measurement coil is for coupling to a second circuit via the second connection conductor, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate.

22. The current sensor according to claim 21, wherein the first connection conductor and the second connection conductor follow, at least partially, the same path.

23. The current sensor according to claim 21 or 22, wherein the first connection conductor and the second connection conductor have, at least partially, the same shape.

24. The current sensor according to any preceding claim, wherein the first connection conductor and the second connection conductor are the same shape.

25. The current sensor according to any of claims 21-24, wherein the first connection conductor and the second connection conductor are coupled such that in use currents flow in the connection conductors in opposite directions.

26. The current sensor according to any of claims 21-25, wherein the first circuit comprises a measurement circuit.

27. The current sensor according to any of claims 21-26, wherein the second circuit comprises a reference circuit.

28. The current sensor according to any of claims 21-27, wherein the substrate further comprises a third layer and a fourth layer, and wherein the first layer, second layer, third layer and fourth layer are provided, in that order, through the substrate.

29. The current sensor according to claim 28, wherein a distance between the first layer and second layer is smaller than a distance between the first layer and the third layer or a distance between the first layer and the fourth layer.

30. The current sensor according to claim 28 or claim 29, wherein a dielectric layer between the first layer and the second layer is smaller than a dielectric layer between the second layer and the third layer.

31. The current sensor according to any of claims 28-30, wherein the first measurement coil is provided across two or more of the four layers of the substrate and the second measurement coil is provided across two or more of the four layers of the substrate.

32. The current sensor according to any of claims 21-31, the current sensor further comprising: a third measurement coil provided on the substrate, the third measurement coil comprising a first end; a fourth measurement coil provided on the substrate, the fourth measurement coil comprising a first end.

33. The current sensor according to claim 32, wherein the connection arrangement further comprises: a third connection conductor provided on the first layer of the substrate, wherein the first end of the third measurement coil is for coupling to a third circuit via the third connection conductor; and a fourth connection conductor provided on the second layer of the substrate, wherein the first end of the fourth measurement coil is for coupling to a fourth circuit the fourth connection conductor, wherein the third connection conductor on the first layer is substantially aligned with the fourth connection conductor in a plane that is perpendicular to a surface of the substrate.

34. The current sensor according to claim 33, wherein the third connection conductor and fourth connection conductor are mirrored versions of the first connection conductor and the second connection conductor.

35. The current sensor according to claim 33 or 34, wherein the first measurement coil is coupled to the second measurement coil and the third measurement coil is coupled to the fourth measurement coil.

36. The current sensor according to any of claims 33-35, wherein the third circuit is the same as the first circuit and the fourth circuit is the same as the second circuit.

37. A connection arrangement for a printed circuit board, PCB, implemented current sensor, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate wherein the first connection conductor is for coupling the PCB implemented current sensor to a first circuit; and a second connection conductor provided on the second layer of the substrate, wherein the second connection conductor is for coupling the PCB implemented current sensor to a second circuit, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor in a plane that is perpendicular to a surface of the substrate.

38. The connection arrangement according to claim 37, wherein the first connection conductor is for coupling to a first measurement coil of the PCB implemented current sensor and the second connection conductor is for coupling to a second measurement coil of the PCB implemented current sensor.

39. A current sensor, the current sensor comprising : a substrate comprising a first layer and a second layer; a first measurement coil provided on the substrate, the first measurement coil comprising a first end; a second measurement coil provided on the substrate, the second measurement coil comprising a first end; a third measurement coil provided on the substrate, the third measurement coil comprising a first end; a fourth measurement coil provided on the substrate, the fourth measurement coil comprising a first end; a connection arrangement, the connection arrangement comprising: a first connection conductor provided on the first layer of the substrate, wherein the first end of the first measurement coil is for coupling to a first circuit via the first connection conductor; and a second connection conductor provided on the second layer of the substrate, wherein the first end of the second measurement coil is for coupling to a second circuit via the second connection conductor, wherein the first connection conductor on the first layer is substantially aligned with the second connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate; a third connection conductor provided on the first layer of the substrate, wherein the first end of the third measurement coil is for coupling to the first circuit via the third connection conductor; and a fourth connection conductor provided on the second layer of the substrate, wherein the first end of the fourth measurement coil is for coupling to the second circuit via the fourth connection conductor, wherein the third connection conductor on the first layer is substantially aligned with the fourth connection conductor on the second layer in a plane that is perpendicular to a surface of the substrate.

40. The current sensor according to claim 39, wherein a second end of the first measurement coil is coupled to a second end of the second measurement coil and a second end of the third measurement coil is coupled to a second end of the fourth measurement coil.

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