Current sensor

Abstract

There is provided a current sensor comprising a first measurement coil and a second measurement coil. The current sensor comprises a substrate comprising a first layer, a second layer, a third layer and a fourth layer, with a first measurement coil provided on the first layer and the third layer of the substrate and a second measurement coil, the second measurement coil provided on the second layer and the fourth layer of the substrate.

Description

[0001] CURRENT SENSOR

[0002] Technical Field

[0003] The present disclosure relates to substrates for current sensors, and in particular to current sensors comprising a first measurement coil and a second measurement coil.

[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 means even a small erroneous signal, picked up from nearby AC conductors, is significant and has 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] There is a need to provide a current sensor implemented on a substrate with a reduced noise in the signal output.

[0011] Summary

[0012] According to an aspect of the invention there is provided a current sensor, the current sensor comprising a substrate comprising a first layer, a second layer, a third layer and a fourth layer, a first measurement coil provided on the first layer and the third layer of the substrate, and a second measurement coil, the second measurement coil provided on the second layer and the fourth layer of the substrate.

[0013] According to another aspect of the invention there is provided a current sensor comprising a substrate comprising a path for a conductor for carrying current, a first measurement coil formed on the substrate and arranged to circumferentially progress around the path for the conductor for carrying current, wherein the first measurement coil comprises a first plurality of loops, a second measurement coil arranged to circumferentially progress around the path for the conductor for carrying current, wherein the second measurement coil comprises a second plurality of loops, wherein the first measurement coil and the second measurement coil are arranged relative to each other such that a respective loop of the first plurality of loops is adjacent to a respective loop of the second plurality of loops in a circumferential direction around the path for the conductor for carrying current.

[0014] According to another aspect of the invention there is provided a current sensor, the current sensor comprising a first output terminal, a second output terminal, a first measurement coil having a first end and a second end, the first end of the first measurement coil coupled to the first output terminal, a second measurement coil having a first end and a second end, the first end of the second measurement coil coupled to the second output terminal, wherein the second end of the first measurement coil is coupled to the second end of the second measurement coil, and configured to be coupled to a reference voltage.

[0015] Brief Description of the Drawings

[0016] 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:

[0017] Figure 1 is a schematic representation of a Rogowski coil;

[0018] Figure 2a is a schematic representation of a differential Rogowski coil in accordance with the invention; Figure 2b is a simplified schematic representation of the Rogowski coil of Figure 2 in accordance with the invention;

[0019] Figure 3 is a four-layer substrate implementation of a differential Rogowski coil in accordance with the invention;

[0020] Figure 4a is a PCB layout of a first measurement coil on two layers of a substrate in accordance with the invention;

[0021] Figure 4b is a PCB layout of a second measurement coil on two layers of a substrate in accordance with the invention;

[0022] Figure 4c is a three-dimensional cut-away view of a portion of the first measurement coil;

[0023] Figure 4d is a three-dimensional cut-away view of a portion of the second measurement coil;

[0024] Figure 5a is a PCB layout of the turns of the first measurement coil on two layers of a substrate with outer circumference advancement in accordance with the invention;

[0025] Figure 5b is a PCB layout of the turns of the second measurement coil on two layers of a substrate with outer circumference advancement in accordance with the invention;

[0026] Figure 5c is a PCB layout combining the coils of Figure 5a and Figure 5b in accordance with the invention;

[0027] Figure 6a is a PCB layout of the turns of the first measurement coil on two layers of a substrate with inner circumference advancement in accordance with the invention;

[0028] Figure 6b is a PCB layout of the turns of the second measurement coil on two layers of a substrate with inner circumference advancement in accordance with the invention;

[0029] Figure 6c is a PCB layout combining the coils of Figure 6a and Figure 6b in accordance with the invention;

[0030] Figure 7a is a PCB layout of the turns of the first measurement coil on two layers of a substrate with central advancement in accordance with the invention;

[0031] Figure 7b is a PCB layout of the turns of the second measurement coil on two layers of a substrate with central advancement in accordance with the invention;

[0032] Figure 7c is a PCB layout combining the coils of Figure 7a and Figure 7b in accordance with the invention;

[0033] Figure 8a is a PCB layout of the turns of the first measurement coil on two layers of a substrate with continuous advancement in accordance with the invention;

[0034] Figure 8b is a PCB layout of the turns of the second measurement coil on two layers of a substrate with continuous advancement in accordance with the invention;

[0035] Figure 8c is a PCB layout combining the coils of Figure 8a and Figure 8b in accordance with the invention;

[0036] Figure 9 is a PCB or substrate stack-up in accordance with the invention;

[0037] Figure 10 is a schematic diagram of capacitive filtering in accordance with the invention;

[0038] Figure 11 is a schematic diagram of the current measurement coils coupled to processing system. Detailed Description

[0039] Known Rogowski coils may be negatively impacted by both electrostatically and magnetically coupled noise. This noise may be noise from current carrying conductors near to the Rogowski coil. The electrostatically coupled noise in a Rogowski coil including multiple coils may be different in each of the 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).

[0040] 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.

[0041] So as to improve the operation of a current sensor, two measurement coils may be implemented on a single printed circuit board or substrate. Both measurement coils act to surround, partially surround or substantially surround a conductor under test (also referred to as a current carrying conductor). The output voltage of a Rogowski coil or measurement coil is proportional to the number of loops or turns of the measurement coil. Providing two coils increases the number of turns and therefore the sensitivity of the system.

[0042] 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. The two measurement coils are provided such that each turn or radial loop of the first measurement coil turns in a first direction (for example a clockwise direction) and each turn or radial loop of the second measurement coil turns in an opposite direction (for example an anti- or counterclockwise direction) from the first terminals of each coil. The second terminals of the coils may be coupled together. Winding the coils with opposite polarities ensures that the first measurement coil picks up a positive voltage and the second coil picks up a negative voltage from the conductor under test. This ensures that the output voltages of the two coils sum differentially, increasing system sensitivity by increasing the output voltage of the coils.

[0043] Additionally, or alternatively to winding each loop of the coils in opposite directions, the first measurement coil and second measurement coil may progress around the conductor in the same direction and follow a similar or adjacent path. 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 into both coils, resulting in a common mode signal that can be easily removed, improving system performance when testing low current without the need to utilise a shield.

[0044] 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.

[0045] 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 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. This coupled noise may then be simply cancelled.

[0046] Rejecting both transverse and lateral external field sources reduces crosstalk, allowing easy integration of the current sensor into harsh environments.

[0047] By following a similar path, the distance between each coil and an external noise source is substantially the same.

[0048] Further, the measurement coils require only two vias per turn or loops, which reduces the implementation cost of the system and increases reliability.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] Figure 2a is a schematic diagram of a current sensor 200 or a device for measuring a current. The current sensor 200 includes a first measurement coil 202 and a second current measurement coil 204. The first current measurement coil 202 has a first end 206 and a second end. The second current measurement coil 204 has a first end 208 and a second end. The second end of the first current measurement coil 202 and the second end of the second current measurement coil 204 are coupled together at a point, terminal or node 210.

[0054] The first current measurement coil 202 and the second current measurement coil 204 are arranged around a conductor 212 under test. The conductor 212 is suitable for carrying a current to be measured by the first current measurement coil 202 and the second current measurement coil 204. When the conductor 212 carries an AC current, a magnetic field generated by the current will induce a voltage across each radial loop or turn of the measurement coils that is proportional to both the magnitude and frequency of the AC current. As such, the first current measurement coil 202 and the second current measurement coil 204 may be considered to be a current sensor or a device for measuring current.

[0055] Figure 2b shows a simplified schematic diagram of the current sensor 200 of Figure 2a. The first current measurement coil 202 and the second current measurement coil 204 are shown in a simplified manner.

[0056] The second ends of the first current measurement coil 202 and the second current measurement coil 204 are coupled together at node 210. The node 210 is coupled to a reference terminal 214, which may be coupled to reference voltage or to ground. The first end 206 of the first current measurement coil 202 is coupled to a first output terminal 216. The first end 208 of the second current measurement coil 204 is coupled to a second output terminal 218.

[0057] Coupling the first current measurement coil 202 and the second current measurement coil 204 in this manner results in the current measurement coils acting as differential current measurement coils. The current measurement coils provide a differential output signal between the first output terminal 216 and the second output terminal 218 and the reference voltage. The first output terminal 216 may be considered to be the positive output or first output of the differential output signal. The second output terminal 218 may be considered to be the negative or second output of a differential output signal.

[0058] The first output terminal 216 and second output terminal 218 may be coupled to a signal processing circuit for further processing. The signal processing circuit may include a differential amplifier. The signal processing circuit may be included on the substrate 302. Alternatively, the signal processing circuit may be a circuit external to the substrate 302.

[0059] 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.

[0060] The first measurement coil 202 may have turns or loops that progress in a clockwise direction from the first end 206 of the first current measurement coil 202. The second measurement coil 204 may have turns or loops that progress in an anti or counter-clockwise direction from the first end 208 of the second current measurement coil 204.

[0061] Alternatively, the turns of the first coil may be wound anti-clockwise and the second coil clockwise. This results in the first measurement coil 202 having an opposite polarity to the second measurement coil 204. This opposite winding polarity is shown by the polarity markers of Figure 2b.

[0062] Winding the first measurement coil 202 and the second measurement coil 204 in this manner results in a positive voltage 220 being induced in the first measurement coil 202 and a negative voltage 222 being induced in the second measurement 204. These induced voltages will difference to create a differential signal that represents the magnetic field from the conductor running through the center of the coils.

[0063] As shown in Figure 2a, the first measurement coil 202 and the second measurement coil 204 form circumferential loops around the conductor under test in the same direction, from their first ends 206, 208 to their second ends 210. Therefore, any pickup from a transverse external magnetic field (such as from an external cable or a noise source) passing through the face of a substrate (which induces a voltage across the circumferential loops of the measurement coils) will result in a common mode voltage that is the same on first 202 and second 204 measurement coils (hence no differential noise voltage is picked up). The common mode rejection ration, CMRR, of a differential amplifier coupled to the first output node 216 and the second output node 218 can remove most of this signal.

[0064] Whilst Figure 2a and Figure 2b show the current sensor coupled in a differential manner, the measurement coils may alternatively be coupled in a single ended manner. For example, first output terminal 216 may act as the output terminal 216, and second output terminal 218 may be coupled to ground or a reference voltage. Terminal 214 may be left unconnected or disconnected. The signal from first output terminal 216 may be coupled or connected to a signal processor or further processing circuitry. Coupling the current sensor in a differential manner provides improved performance when compared to a single-ended connection of the current sensor.

[0065] Figure 3 shows a printed circuit board, PCB, implementation 300 of the current sensor 200 shown in Figures 2a and 2b. The printed circuit board 300 comprises a substrate 302 comprising four layers.

[0066] The substrate 302 comprises a first plurality of vias 304 arranged around an inner circumference of the first measurement coil 202 and a second plurality of vias 306 arranged around an inner circumference of the second measurement coil 204. The first plurality of vias 304 and the second plurality of vias 306 may be arranged around the same circumference or arranged around concentric circumferences. Arranging the vias around concentric circumferences improves the electrostatic coupling performance, as the conductor under test will be equidistant to both measurement coils. The vias may be arranged in a non-concentric manner, allowing the vias to be fit more densely on the substrate. Whilst this may have an impact on electrostatic coupling performance, providing a denser via arrangement allows a greater number of loops or turns to be provided for each measurement coil.

[0067] The substrate 302 further comprises a third plurality of vias 320 arranged around an outer circumference of the first measurement coil 202 and a fourth plurality of vias 322 arranged around an outer circumference of the second measurement coil 204. The third plurality of vias 320 and the fourth plurality of vias 322 may be arranged around the same circumference or arranged around concentric circumferences. The inner circumference has a smaller diameter than the outer circumference. The current sensor 300 includes a conductor 212 for carrying a current to be measured by the first current measurement coil 202 and the second current measurement coil 204. The conductor 212 is implemented along a path 308 of the substrate 302. The path 308 may be an aperture for receiving the conductor 212. Alternatively, the conductor 212 may be a conductive trace running through the substrate, with no aperture present.

[0068] The first current measurement coil 202 and the second current measurement coil 204 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 302 are represented using different line formats.

[0069] The first current measurement coil 202 is implemented on the first and third layers of the substrate 302. The second current measurement coil 204 is implemented on the second and fourth layers of the substrate 302.

[0070] Each layer of the substrate 302 comprises a plurality of measurement conductors. A first plurality 310 of measurement conductors are located on a first layer of the substrate 302. A second plurality 312 of measurement conductors are located on a second layer of the substrate 302. A third plurality 314 of measurement conductors are located on a third layer of the substrate 302. A fourth plurality 316 of measurement conductors are located on a fourth layer of the substrate 302.

[0071] The third plurality of measurement conductors 314 and the fourth plurality of measurement conductors 316 cannot be seen in Figure 3, as the first plurality of measurement conductors 310 are aligned with the third plurality of measurement conductors 314, and the second plurality of measurement conductors 312 are aligned with the fourth plurality of measurement conductors 316. These conductors can be seen in Figures 5a-5c, which show the conductors in a slightly mis-aligned state for ease of understanding.

[0072] The substrate 302 further comprises a plurality of circumferential progression conductors 318. The circumferential progression conductors are arranged to provide circumferential progression for the first current measurement coil 202 and the second current measurement coil 204.

[0073] The circumferential progression conductors of the first measurement coil 202 are on the first and third layers of the substrate. The circumferential progression conductors of the second measurement coil 204 are provided on the second and fourth layers of the substrate. As the circumferential progression conductors of the two measurement coils cross over each other (as shown in Figure 3) if they were on the same layers of the substrate, additional vias would be required to prevent them interacting with or obstructing each other.

[0074] Providing the first measurement coil and second measurement coil on different layers of the substrate, and in particular providing the circumferential progression of the first and second measurement coils on different layers of the substrate, ensures that the circumferential progression conductors of the first measurement coil do obstruct, impede or interact with those of the second measurement coil. As such, only two vias are needed per turn or loop of each measurement coil. This reduces the manufacturing complexity of the system and ensures that the loop areas of the two measurement coils are matched, as only a minimal number of vias, which may change the loop shape or size, are required.

[0075] Whilst the first measurement coil is described as being provided on the first and third layers of the substrate, and the second measurement coil is described as being provided on the second and fourth layers of the substrate, it should be understood that the coils may be provided on different layers. For example, the first measurement coil may be provided on the first and fourth layers of the substrate and the second measurement coil may be provided on the second and third layers of the substrate. Whilst this may reduce the matching between the coils (in that one of the coils will have slightly different loop areas), if the distances between the layers are small, the mismatch may be acceptable in some situations. The provision of the measurement coils across different layers of the substrate ensures that the circumferential progression conductors and vias do not clash or interfere with one another. Alternatively, the measurement coils may be implemented across four layers of a substrate or PCB which includes more than four layers.

[0076] Figures 4a and 4b show subsections of the PCB implementation of a current sensor 300 of Figure 3.

[0077] Figure 4a includes only the vias and conductive traces used to form the first measurement coil 202. The substrate 302 comprises a first plurality of vias 304 arranged around an inner circumference of the first measurement coil 202. The substrate further comprises the third plurality of vias 320 arranged around an outer circumference of the first measurement coil 202,

[0078] Figure 4b shows the vias and conductive traces used to form the second measurement coil 204. The substrate comprises the second plurality of vias 306 arranged around an inner circumference of the second measurement coil 204. The substrate 302 further comprises the fourth plurality of vias 322 arranged around an outer circumference of the second measurement coil 204. The inner circumferences have smaller diameters than the outer circumference. Whilst the first plurality of vias 304 and the second plurality of vias are shown on the same circumference, the first and second plurality of vias may be on concentric circumferences. Further, the third 320 and fourth 322 plurality of vias may be on concentric circumferences. The inner and outer circumferences of the first and second measurement coil may refer to circumferences around the conductor 212 or the path for the conductor 308.

[0079] Figure 4c shows a 3-dimensional subsection of the first measurement coil 202 implemented on the first and third layers of the substrate. Figure 4d shows a 3-dimensional subsection of the second measurement coil 204 provided on the second and fourth layers of the substrate. These figures show clearly the turn direction of the loops of the first measurement coil 202 and the second measurement coil 204. The Figures include arrows that indicate the direction of progression of the loops of the measurement coils.

[0080] The first measurement coil 202 begins at a first end 206 and the loops of the first measurement coil 202 progress in a first direction from the first end 206. In figure 4c, the loops progress in a counterclockwise direction from the first end 206, however this purely exemplary, and they could progress in a clockwise direction.

[0081] The second measurement coil 204 begins at a first end 208, and the loops of the second measurement coil 204 progress in a second direction from the first end 208. The second direction is an opposite direction to the first direction of the loops of the first measurement coil 202. In figure 4d, the loops of the second measurement coil 204 progress in a clockwise direction from the first end 208, however this is purely exemplary, and they could alternatively progress in an anti- or counterclockwise direction.

[0082] As described, having an opposite rotation or turn direction of the loops of the first 202 and second 204 measurement coils ensures that the first measurement coil 202 picks up a positive voltage and the second coil 204 picks up a negative voltage (or vice versa) from the conductor under test. This ensures that the output voltages of the two coils sum differentially, increasing system sensitivity by increasing the output voltage of the coils.

[0083] The circumferential progression shown in Figures 4c and 4d is around a circumference of the measurement coils, however it should be understood that the circumferential progression conductors may instead progress in both circumferential and radial directions, as shown in Figures 5a-5c.

[0084] Figure 5a shows a simplified subsection of the conductive traces of the first measurement coil 202 of Figure 4a. Figure 5b shows a simplified subsection of the conductive traces of the second measurement coil 202 of Figure 4b. Figure 5c shows a simplified subsection of the conductive traces of Figure 3, showing in particular how the first current measurement coil 202 and the second current measurement coil 204 may be combined in an interleaved fashion to form a differential current sensor. A legend is provided on the figure, wherein the conductors on different layers of the substrate are represented using different line formats.

[0085] Measurement conductors on the first layer and third layer, and on the second layer and the fourth layer are represented as being adjacent to each other, rather than directly in the same plane, for ease of understanding. However, it should be understood that the first and third plurality of measurement conductors are aligned in radial planes and the second and fourth plurality of measurement conductors are aligned in radial planes.

[0086] Figure 5a shows a subsection of the first current measurement coil 202 implemented on the first layer of the substrate and the third layer of the substrate.

[0087] The first plurality of measurement conductors and the third plurality of measurement conductors are coupled by respective vias of the first plurality of vias 304 and the third plurality of vias 320, so as to form the first measurement coil 202.

[0088] A first turn or loop of the first current measurement coil 202 comprises a measurement conductor 502 of the first plurality of measurement conductors 310 formed on the first layer of the substrate, and a measurement conductor 504 of the third plurality of measurement conductors 314 formed on the third layer of the substrate. Measurement conductor 502 and 504 are positioned or located in the same plane through the substrate. The measurement conductor 502 and the measurement conductor 504 are coupled at a first end (an end closer to the aperture, path or current carrying conductor) of the measurement conductors by a via 506 of the first plurality of vias 304 at the inner circumference of the first measurement coil 202.

[0089] A second turn or loop of the first current measurement coil 202 comprises a measurement conductor 508 of the first plurality of measurement conductors 310 formed on the first layer of the substrate, and a measurement conductor 510 of the third plurality of measurement conductors 314 formed on the third layer of the substrate. The measurement conductor 508 and the measurement conductor 510 are coupled at a first end (an end closer to the aperture, path or current carrying conductor) of the measurement conductors by a via 512 of the first plurality of vias 304 at the inner circumference of the first measurement coil.

[0090] The vias shown in Figures 5a-5c, and in the following figures, are depicted as being in straight lines. This is for ease of understanding. The vias of the first plurality of vias 304 and the second plurality of vias 306 may instead follow a circumference, as shown in Figure 3. At the exterior circumference, circumferential progression of the first measurement coil 202 is provided using circumferentially progressing elements which connect the measurement conductors to respective vias of the third plurality of vias 320 at the outer circumference. These circumferential progression conductors 318 allow the measurement coils to progress from a first end of the current measurement coils to the second end of the current measurement coils. This allows the measurement coil to surround or substantially surround the conductor 212. Whilst the measurement coil may travel 360 degrees around the substrate or conductor, the measurement coils may instead travel substantially 360 degrees, for example 340, 345, 350, 355 degrees, or any value between 340-360 degrees. This allows space for external hook-ups or connections to be included. A large opening or aperture 308 may be included to allow the conductor under test to be inserted, such that the aperture 308 has a diameter or width that is greater than the diameter of the conductor to be measured 212.

[0091] The measurement conductor 504 is coupled to the via 514 of the third plurality of vias 320 using a first circumferential progression conductor 516 of the plurality of circumferential progression conductors or circumferential advancement conductors 318. The via 514 is coupled to the measurement conductor 508 via a second circumferential progression conductor 518.

[0092] The circumferential progression conductors provide the first measurement coil 202 with a circumferential progression around the substrate 302. This allows the first measurement coil 202 to substantially surround the conductor 212 for carrying a current. The measurement conductors are arranged radially from the centre of the substrate. The circumferential progression conductors are located adjacent to and directly connected to the second plurality of vias at the outer circumference of the substrate. The plurality of circumferential progression conductors 318 form an advancement or progression region of the measurement coil. The advancement region is closer to the third 320 and fourth 322 plurality of vias than to the first 304 and second 306 plurality of vias 320, such that the advancement region is closer to, or adjacent to, an outer circumference of the measurement coils than the inner circumference of the measurement coils.

[0093] Figure 5b shows a subsection of the second current measurement coil implemented on the second layer of the substrate and the fourth layer of the substrate 302.

[0094] A first turn or loop of the second current measurement coil 204 comprises a conductor 520 of the fourth plurality of measurement conductors formed on the fourth layer of the substrate, and a measurement conductor 522 of the second plurality of measurement conductors 306 formed on the second layer of the substrate. The measurement conductor 520 and the measurement conductor 522 are coupled at a first end (an end closer to the aperture, path or current carrying conductor) of the measurement conductors by a via 524 of the second plurality of vias 306 at the inner circumference of the second measurement coil 204.

[0095] A second turn or loop of the second current measurement coil 202 comprises a measurement conductor 526 of the fourth plurality of measurement conductors formed on the fourth layer of the substrate, and a measurement conductor 528 of the second plurality of measurement conductors formed on the second layer of the substrate. The measurement conductor 526 and the measurement conductor 528 are coupled at a first end (an end closer to the aperture, path or current carrying conductor) of the measurement conductors by a via 530 of the second plurality of vias 306 at the inner circumference of the second measurement coil 204.

[0096] The first turn or loop of the second current measurement coil 204 and the second turn or loop of the second current measurement coil 204 are coupled together at the fourth plurality of vias 322 at the outer circumference of the substrate.

[0097] The measurement conductor 522 is coupled to the via 532 of the fourth plurality of vias 322 using a first circumferential progression conductor 534. The via 532 is coupled to the measurement conductor 526 via a second circumferential progression conductor 536.

[0098] Figure 5c shows a subsection of the current sensor including both the first measurement coil 202 implemented on the first layer and the third layer of the substrate and the second measurement coil 204 implemented on the second layer and the fourth layer of the substrate.

[0099] A first turn 538 of the first measurement coil 202 is located adjacent to a first turn 540 of the second measurement coil. A second turn 542 of the first measurement coil 202 is located adjacent to a second turn 544 of the second measurement coil. The turns of the measurement coils progress in this order around the substrate, with a turn or loop of the first measurement coil 202 being followed by or adjacent to a turn or loop of the second measurement coil 204. Providing the turns in this adjacent interleaved manner improves the rejection capabilities of the coils, as they follow similar paths around the conductor.

[0100] Alternatively, a first turn of the first measurement coil 202 may be located adjacent to a second turn of the first measurement coil 202. The second turn of the first measurement coil may be adjacent to a first turn of the second measurement coil 204, which is itself adjacent to a second turn of the second measurement coil 204. This pattern may be repeated around the substrate. The coils may also be provided such that 3, 4, 5, 6 or more turns of each coil are adjacent to one another, and followed by the same number of adjacent turns of the other coil.

[0101] As shown in Figure 5, the turns or loops of the first measurement coil 202 and the second measurement coil 204 are provided in adjacent radial planes, rather than in the same radial plane. By doing this, the measurement conductors of one of the coils are not located in the same plane as the measurement conductors of the other coil. If an external noise source were located above the substrate 302, both the first measurement coil 202 and the second measurement coil would see almost the same capacitive coupling from the noise source, resulting in the same or a similar noise in each coil. This would allow the noise to be cancelled at the differential output.

[0102] If a measurement conductor of the first measurement coil 202 was located in the same plane as a measurement conductor of the second measurement coil 204, the measurement conductor of the first measurement coil 202 may block or reduce the capacitive coupling of the noise into the conductor of the second measurement coil 204. This would result in different capacitive noise coupling into the two coils, and thus the noise would not cancel. Locating the turns adjacent to one another, such that they are in separate or independent planes, provides more even or equal capacitive coupling into the two measurement coils.

[0103] Whilst the positioning of the turns of the first 202 and second 204 measurement coils in adjacent radial planes has been described with respect to Figure 5, it should be understood that this may be applied to any of the measurement coil implementations or layouts described throughout the description.

[0104] The measurement coils may also be provided on multiple PCBs or substrates so that they can be separated to insert the conductor and then re-assembled to make the coil again. For example, one substrate may contain a 180-degree version of the first measurement coil 202 and the second measurement coil, starting from a common reference and finishing with 2 outputs on that board. This first substrate can then be attached to a second substrate through a connector or a pogo-pin. As such, only two connections are required between the substrates. The second substrate may include the first measurement coil 202 and the second measurement coil 204 continuing for another 180 degrees, with the first measurement coil 202 and the second measurement coil 204 starting from the 2 end points or outputs of the first board and finishing at 2 end points of the second board. The end points or outputs of the second board provide a signal which contains the sum of the signals picked up on the first and second boards. The first substrate or second substrate may comprise an amplifier or processing circuitry coupled to the first and second measurement coils. This split-coil arrangement may be applied to any of the current sensors described throughout this description. This arrangement allows a clamp on type coil that has the same properties as a full 360- degree coil regarding external field rejection and electrostatic coupling. This can be further improved by stacking 4 boards, with the 1stand 4thboard sandwiching the 2ndand 3rdboards, so that the average of them is the same as for the other two with respect to a vertical magnetic field. This also helps the stack be resilient to a tilt in the conductor. In an arrangement with multiple boards the pair of conductors need to be cascaded down the stack, so that they are all in series, allowing the output to be the sum of boards 1 + 2+3+4. As such, the substrates or boards need to be combined so that boards 1 and 2 are in series and boards 3 and 4 are in series. These boards are then coupled in parallel so that the output is the average of boards 1+2 with boards 3+4.

[0105] The first turn or loop of the first current measurement coil 202 and the second turn or loop of the first current measurement coil 202 are coupled together at the third plurality of vias 320 at the outer circumference of the first measurement coil 202.

[0106] As shown in Figures 5a-5c, the first measurement coil is provided across a first and third layer of the substrate, whilst the second measurement coil is provided across a second and fourth layer of the substrate. However, it should be understood that each measurement coil may be provided across more than two layers of the substrate. The layers referenced here may refer to the order the layers are provided on the substrate, such that the first layer may be a top layer of the four layers, the second layer below the first layer, the third layer below the second layer and the fourth layer below the third layer, in that order. Other layers may be provided around, on top, below or between the referenced layers.

[0107] For example, instead of the arrangement shown in Figure 5, the first measurement coil may be provided across layers one and four and the second measurement coil provided across layers two and three. This may result in a slight imbalance in the first and second measurement coils, as the distance between the first and fourth layers is greater than that between the second and third layers. This means that the loop area of the first measurement coil is larger than that of the second measurement coil. This layout be used in situations where the imbalance in loop area has limited effect.

[0108] Alternatively, each measurement coil may be provided across all four layers, in an alternating manner. For example, a first plurality of loops or turns of the first measurement coil may be provided on two of the four layers (e.g. layers 1-3, 2-4, 1-4, or 2-3) and a second plurality of loops or turns of the first measurement coil may be provided on the other two of the four layers that the first plurality of loops is not provided on (e.g. layers 1- 3, 2-4, 1-4, 2-3). The pattern formed by this alternating arrangement may be provided in a repeating pattern. For example, the pattern or layout may be repeated every turn. For example, each turn of the first plurality of turns may be followed by a turn of the second plurality of turns. Alternatively, a plurality of turns of the first plurality of turns may be followed by a plurality of turns of the second plurality of turns.

[0109] The second measurement coil may be provided in a corresponding manner.

[0110] Alternating the turns in this fashion ensures that each coil is spread across all four layers of the substrate. In the conductor that is provided through the path of the current sensor, that is being sensed by the current sensor, travels parallel to the surface of the substrate before passing through the path, then the coupling into both coils will be the same, as the coils spend, on average, the same proportion of the coil on each layer of the substrate. This ensures that the electrostatic coupling is matched. Further, for non-constant magnetic field noise sources, the noise source will be the same distance to both the first measurement coil and the second measurement coil.

[0111] Alternating the layers that the coils are provided on, as described above, may be applied to any of the coil layouts described in this description.

[0112] Figures 3-5c show a current sensor where circumferential progression, or advancement, of the measurement coil is provided at an outer circumference of the measurement conductors, adjacent to the second plurality of vias. However, circumferential progression may take place at various locations of the measurement coil. For example, circumferential progression conductors may be provided adjacent to the inner circumference of the measurement coils (adjacent to the first and second plurality of vias), adjacent to the outer circumference of the measurement coils (adjacent to the third and fourth plurality of vias) or at a location between the inner and outer circumferences.

[0113] Adjacent to the inner circumference may mean that the circumferential progression conductors are closer to the inner circumference than the outer circumference. Similarly, adjacent to the outer circumference may mean that the circumferential progression conductors are closer to the outer circumference than the inner circumference. A location between the inner and outer circumference may mean that the circumferential progression conductors are equi-distant form the inner and outer circumferences.

[0114] Figures 6a-6c show simplified subsections of measurement coils where circumferential progression takes place adjacent to the first plurality of vias 304 at the inner circumference. Figure 6a shows a simplified subsection of the conductive traces of the first measurement coil 202. Figure 6b shows a simplified subsection of the conductive traces of the second measurement coil 202. Figure 6c shows a simplified subsection of the conductive traces of both the first current measurement coil 202 and the second current measurement coil 204 combined in an interleaved fashion to form a differential current sensor. A legend is provided on the figure, wherein the conductors on different layers of the substrate are represented using different line formats. The teachings of Figures 3-5C applies equally to the measurement coils shown in Figures 6a-6c, and as such will not be repeated in detail here.

[0115] Figure 6a shows a subsection the first current measurement coil implemented on the first layer of the substrate and the third layer of the substrate.

[0116] A first turn or loop of the first current measurement coil 202 comprises a measurement conductor 602 of the third plurality of measurement conductors 320 formed on the third layer of the substrate, and a measurement conductor 604 of the first plurality of measurement conductors 304 formed on the first layer of the substrate. The measurement conductor 602 and the measurement conductor 604 are coupled at a second end (an end further from the aperture, path or current carrying conductor) of the measurement conductors by a via 606 of the third plurality of vias 320 at the outer circumference of the measurement coil.

[0117] A second turn or loop of the first current measurement coil 202 comprises a measurement conductor 608 of the third plurality of measurement conductors 320 formed on the third layer of the substrate 302, and a measurement conductor 610 of the first plurality of measurement conductors 304 formed on the first layer of the substrate 302. The measurement conductor 608 and the measurement conductor 610 are coupled at a second end (an end further from the aperture, path or current carrying conductor) of the measurement conductors by a via 612 of the third plurality of vias 320 at the outer circumference of the measurement coil.

[0118] At the inner circumference, circumferential progression of the first measurement coil 202 is provided using the plurality of circumferentially progressing elements or conductors 318 which connect the measurement conductors to respective vias of the first plurality of vias 304 at the inner circumference of the measurement coil. These circumferential progression conductors 318 allow the measurement coils to progress from a first end of the current measurement coils to the second end of the current measurement coils.

[0119] The first turn or loop of the first current measurement coil 202 and the second turn or loop of the first current measurement coil 202 are coupled together at the first plurality of vias 304 at the inner circumference of the measurement coil.

[0120] The measurement conductor 604 is coupled to the via 614 of the first plurality of vias 304 using a first circumferential progression conductor 616. The via 614 is coupled to the measurement conductor 608 via a second circumferential progression conductor 618. Figure 6b shows a subsection the second current measurement coil implemented on the second layer of the substrate and the fourth layer of the substrate.

[0121] A first turn or loop of the second current measurement coil 204 comprises a conductor 620 of the second plurality of measurement conductors 306 formed on the second layer of the substrate, and a measurement conductor 622 of the fourth plurality of measurement conductors 322 formed on the fourth layer of the substrate. The measurement conductor 620 and the measurement conductor 622 are coupled at a second end (an end further from the aperture, path or current carrying conductor) of the measurement conductors by a via 624 of the fourth plurality of vias 322 at the outer circumference of the measurement coil.

[0122] A second turn or loop of the second current measurement coil 202 comprises a measurement conductor 626 of the second plurality of measurement conductors 306 formed on the second layer of the substrate, and a measurement conductor 628 of the fourth plurality of measurement conductors formed on the fourth layer of the substrate. The measurement conductor 626 and the measurement conductor 628 are coupled at a second end (an end further from the aperture, path or current carrying conductor) of the measurement conductors by a via 630 of the fourth plurality of vias 322 at the outer circumference of the measurement coil.

[0123] The first turn or loop of the second current measurement coil 204 and the second turn or loop of the second current measurement coil 204 are coupled together at the second plurality of vias 306 at the inner circumference of the measurement coil.

[0124] The measurement conductor 622 is coupled to the via 632 of the second plurality of vias 306 using a first circumferential progression conductor 634. The via 632 is coupled to the measurement conductor 626 via a second circumferential progression conductor 636.

[0125] Figure 6c shows a subsection of the current sensor including both the first measurement coil 202 implemented on the first layer and the third layer of the substrate and the second measurement coil 204 implemented on the second layer and the fourth layer of the substrate.

[0126] A first turn 638 of the first measurement coil 202 is located adjacent to a first turn 640 of the second measurement coil. A second turn 642 of the first measurement coil 202 is located adjacent to a second turn 644 of the second measurement coil. The turns of the measurement coils progress in this order around the substrate, with a turn or loop of the first measurement coil 202 being followed by or adjacent to a turn or loop of the second measurement coil 204. In the current sensor of Figures 6a-6c, circumferential progression is provided using circumferential conductors adjacent to the first plurality of vias and the second plurality of vias at the inner circumference of them measurement coils. The advancement region is closer to the first 304 and second 306 plurality of vias 320 than to the third 320 and fourth 322 plurality of vias, such that the advancement region is closer to, or adjacent to, an inner circumference of the measurement coils than to the outer circumference of the measurement coils. More specifically, the circumferential progression conductors may be directly coupled to the inner circumference vias 302, 306.

[0127] Providing the advancement or circumferential progression of the first measurement coil 202 and the second measurement coil 204 at the inner circumference of the measurement coil reduces the length of the circumferential loop formed by the circumferential conductors. Reducing the size of the circumferential loop reduces the common mode signal coupled into the first measurement coil 202 and the second measurement coil 204 by external transverse fields, compared to a current sensor where the circumferential advancement occurs adjacent to the second plurality of vias at the outer circumference of the substrate. This reduces noise coupled into the system, improving the signal-to-noise ratio SNR.

[0128] Figures 7a-7c show simplified subsections of measurement coils where circumferential progression takes place part-way, half-way or centrally between the first plurality of vias 304 and the second plurality of vias 306. Figure 7a shows a simplified subsection of the conductive traces of the first measurement coil 202. Figure 7b shows a simplified subsection of the conductive traces of the second measurement coil 202. Figure 7c shows a simplified subsection of the conductive traces of both the first current measurement coil 202 and the second current measurement coil 204 combined in an interleaved fashion to form a differential current sensor. A legend is provided on the figure, wherein the conductors on different layers of the substrate are represented using different line formats.

[0129] Figure 7a shows a subsection the first current measurement coil implemented on the first layer of the substrate and the third layer of the substrate.

[0130] A first turn or loop of the first current measurement coil 202 comprises a measurement conductor 702 and a measurement conductor 704 of the first plurality of measurement conductors formed on the first layer of the substrate. Measurement conductor 702 is coupled to measurement conductor 704 by a first circumferential progression conductor 706. The first turn or loop further comprises a measurement conductor 708 and a measurement conductor 710 of the third plurality of measurement conductors 314. Measurement conductor 704 is coupled to measurement conductor 708 by a second circumferential progression conductor 710. Measurement conductor 704 is coupled to measurement conductor 708 using a via 714 of the first plurality of vias 304. This first turn of the first measurement coil is coupled to a second turn using via 716 of the third plurality of vias 320.

[0131] Figure 7b shows a subsection the second current measurement coil implemented on the second layer of the substrate and the fourth layer of the substrate.

[0132] A first turn or loop of the second current measurement coil 202 comprises a measurement conductor 718 and a measurement conductor 620 of the fourth plurality of measurement conductors 716 formed on the fourth layer of the substrate. Measurement conductor 718 is coupled to measurement conductor 720 by a first circumferential progression conductor 722. The first turn or loop further comprises a measurement conductor 724 and a measurement conductor 726 of the second plurality of measurement conductors 312. Measurement conductor 724 is coupled to measurement conductor 726 by a second circumferential progression conductor 728. Measurement conductor 720 is coupled to measurement conductor 724 using a via 730 of the second plurality of vias 306. This first turn of the first measurement coil is coupled to a second turn using via 732 of the fourth plurality of vias 322.

[0133] Figure 7c shows a subsection of the current sensor including both the first measurement coil 202 implemented on the first layer and the third layer of the substrate and the second measurement coil 204 implemented on the second layer and the fourth layer of the substrate.

[0134] A first turn 738 of the first measurement coil 202 is located adjacent to a first turn 740 of the second measurement coil. A second turn 742 of the first measurement coil 202 is located adjacent to a second turn 744 of the second measurement coil. The turns of the measurement coils progress in this order around the substrate, with a turn or loop of the first measurement coil 202 being followed by or adjacent to a turn or loop of the second measurement coil 204.

[0135] In the current sensor of Figures 7a-7c, circumferential progression is provided using circumferential conductors located between the first / second plurality of vias and the third / fourth plurality of vias. The advancement region may be centrally located between the inner and outer via circumferences. Put another way, the advancement region may be provided such that the circumferential progression conductors are coupled to radial measurement conductors on both ends of the circumferential progression conductors.

[0136] The substrate or PCB implementations of the current measurement coils shown in Figures 5a-7c show the turns of the first measurement coil 202 and the second measurement coil 204 as being adjacent to one another. Figures 5a-7c show measurement coils comprising circumferential progression conductors providing the advancement of the coil. These circumferential progression conductors are located at the outer circumference in Figures 5a-5c, at the inner circumference in Figures 6a-6c and in between the inner and outer circumferences in Figures 7a-7c. However, a measurement coil may include circumferential progression conductors providing the advancement of the coil at a combination of the inner circumference, outer circumference and in-between the circumferences. For example, a measurement coil may include circumferential progression or advancement at both the outer circumference and at the inner circumference, with the measurement conductors coupled at both ends to circumferential progression conductors, rather than at a single end.

[0137] Whilst Figures 5a-7c show measurement coils comprising radially extending measurement conductors and circumferential progression conductors providing the advancement of the coil, these conductors may instead be combined into a single conductor that provides both radial and circumferential progression. These combined conductors result in each turn of the current measurement coil requiring only two conductors.

[0138] Figures 8a-8c show simplified subsections of measurement coils where circumferential progression takes place using the measurement conductors, such that the measurement conductors provide both radial and circumferential advancement. Figure 8a shows a simplified subsection of the conductive traces of the first measurement coil 202. Figure 8b shows a simplified subsection of the conductive traces of the second measurement coil 202. Figure 8c shows a simplified subsection of the conductive traces of both the first current measurement coil 202 and the second current measurement coil 204 combined in an interleaved fashion to form a differential current sensor. A legend is provided on the figure, wherein the conductors on different layers of the substrate are represented using different line formats.

[0139] Figure 8a shows a subsection the first current measurement coil implemented on the first layer of the substrate and the third layer of the substrate.

[0140] A first turn or loop of the first current measurement coil 202 comprises a measurement conductor 802 of the first plurality of measurement conductors formed on the first layer of the substrate, and a measurement conductor 804 of the third plurality of measurement conductors formed on the third layer of the substrate. The measurement conductor 802 and the measurement conductor 804 are coupled at a first end (an end nearer to the aperture, path or current carrying conductor) of the measurement conductors by a via 806 of the first plurality of vias 304 at the inner circumference of the measurement coil. A second turn or loop of the first current measurement coil 202 comprises a measurement conductor 810 of the first plurality of measurement conductors formed on the first layer of the substrate, and a measurement conductor 812 of the third plurality of measurement conductors formed on the third layer of the substrate. The measurement conductor 810 and the measurement conductor 812 are coupled at a first end (an end nearer to the aperture, path or current carrying conductor) of the measurement conductors by a via 814 of the first plurality of vias 304 at the inner circumference of the measurement coil.

[0141] The two turns of the measurement coil are coupled to each other by a via 808 of the third plurality of vias 320 at the outer circumference of the substrate.

[0142] Figure 8b shows a subsection the second current measurement coil implemented on the second layer of the substrate and the fourth layer of the substrate.

[0143] A first turn or loop of the first current measurement coil 202 comprises a measurement conductor 816 of the fourth plurality of measurement conductors formed on the fourth layer of the substrate, and a measurement conductor 818 of the second plurality of measurement conductors formed on the second layer of the substrate. The measurement conductor 816 and the measurement conductor 818 are coupled at a first end (an end nearer to the aperture, path or current carrying conductor) of the measurement conductors by a via 820 of the second plurality of vias 306 at the inner circumference of the measurement coil.

[0144] A second turn or loop of the first current measurement coil 202 comprises a measurement conductor 824 of the fourth plurality of measurement conductors formed on the fourth layer of the substrate, and a measurement conductor 826 of the second plurality of measurement conductors formed on the second layer of the substrate. The measurement conductor 824 and the measurement conductor 826 are coupled at a first end (an end nearer to the aperture, path or current carrying conductor) of the measurement conductors by a via 828 of the second plurality of vias 306 at the inner circumference of the measurement coil.

[0145] The two turns of the second measurement coil 204 are coupled to each other by a via 822 of the fourth plurality of vias 322 at the outer circumference of the measurement coil.

[0146] Figure 8c shows a subsection of the current sensor including both the first measurement coil 202 implemented on the first layer and the third layer of the substrate and the second measurement coil 204 implemented on the second layer and the fourth layer of the substrate.

[0147] A first turn 830 of the first measurement coil 202 is located adjacent to a first turn 640 of the second measurement coil. A second turn 642 of the first measurement coil 202 is located adjacent to a second turn 644 of the second measurement coil. The turns of the measurement coils progress in this order around the substrate, with a turn or loop of the first measurement coil 202 being followed by or adjacent to a turn or loop of the second measurement coil 204.

[0148] The measurement conductors used in the current measurement coils of 8a-8c do not extend in radial planes through the substrate, instead they extend at a non-zero angle to the radial plane from the centre of the measurement coil. For example, the measurement conductors are positioned at an angle between 5 degrees - 45 degrees from the radial plane, such as a 20-degree, 25-degree or 30-degree angle from the radial plane. In this way, both the radial progression forming the loops or turns of the current measurement coils, and the circumferential progression of the measurement coils are provided using a single set of measurement conductors.

[0149] Each turn of the measurement coils shown in Figures 5a-8c includes either a single via of the first plurality of vias and a single via of the third plurality of vias or a single via of the second plurality of vias and a single via of the fourth plurality of vias. This provides an efficient measurement coil layout, with a minimum number of vias (two vias) being required per turn. This allows the manufacture of the current sensors to be simpler and provides a high measurement coil gain per unit area of substrate or printed circuit board. Further, all parts of the measurement conductors in the measurement coil result in additional measurement coil sensitivity, with no part of the measurement conductors subtracting from the output signal of the current sensor.

[0150] It will be appreciated that both the inner and outer vias may not be exactly on the circumference - alternate pairs of the vias may be staggered to accommodate a tighter packing distance, or they may not be exactly at the circumference to accommodate other components or coils or to meet mechanical constraints.

[0151] Figure 9 shows a planar view or cross-sectional cut-through of the stack-up or layer-order of a substrate 900. The current sensors of the preceding are implemented across four layers of a substrate. The substrate 900 may be used in the current measurement coils according to any of the preceding figures.

[0152] Substrate 900 comprises a first layer 902, a second layer 904, a third layer 906 and a fourth layer 908 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 900. The first layer 902 and the second layer 904 are separated by a first distance 910. The second layer 904 and the third layer 906 are separated by a second distance 912. The third layer 906 and the fourth layer 908 are separated by a third distance 914. The first distance 910 and the third distance 914 are substantially the same distance. For example, the first distance 910 and the third distance 914 may be 0.1mm. Alternatively, the first distance 910 and the third distance 914 may be 0.2mm, 0.3mm etc. The second distance 912 is larger than the first distance 910 and the third distance 914. For example, the second distance may be 1.7mm, alternatively, the second distance may be 1.5mm, 2mm or l-2mm. As such, a distance between the first layer and the second layer is less than a distance between the second layer and the third layer; and wherein a distance between the third layer and the fourth layer is less than the distance between the second layer and the third layer. This distances between the layers of the substrate may be determined based on manufacturing processes.

[0153] Implementing the first measurement coil on the first layer 902 and the third layer 906, and the second measurement coil on the second layer 904 and fourth layer 908 ensures that the radial loop area or area enclosed by a turn of the first measurement coil is the equivalent to the area enclose by a turn of the second measurement coil.

[0154] Further, this ensures that almost the entire substrate thickness is used for the coil radial turns of both the first measurement coil 202 and the second measurement coil 204. This maximises the average radial loop area, which maximises the voltage induced in the loop for a given substrate thickness.

[0155] Further, the distance between the average position of the radial loops of the first measurement coil 202 and the second measurement coil 204 is minimised, such that the radial loops are on average separated by a distance equal to the first distance 910 or the third distance 914. This ensures that the voltage induced due to an external transverse alternating magnetic field across the large circumferential loop formed by the circumferential progression conductors in the advancement region of the first measurement coil 202 and the second measurement coil 204 is very close to equal, even in the presence of a non-uniform field. The electrostatic coupling to the first and second measurement coils from a nearby conductor, above or below the substrate, with a potential difference, will also be very close to equal for both coils.

[0156] Whilst the substrate 302 is described as having four layers, the substrate may have four or more layers, where the current sensor is implemented across four layers of the substrate 302. For example, in a 6-layer board, the current sensor may be implemented on layers 2 and 4 and 3 and 5 while layers 1 and 6 are used for power and ground routing or for components. Layers 1 and 6 may alternatively or additionally carry current into the centre of the coil and through power vias to a conductor coming out the other side, once, or multiple times to provide multiple primary windings. Layers 1 and 6 may additionally or alternatively comprise electrostatic shield, for example they may comprise a ground plane across the layer. The ground plane may be a flooded layer of the substrate. This provides a PCB implemented current carrying conductor 212.

[0157] Figure 10 shows a current sensor comprising capacitors. The capacitors of Figure 10 may be implemented in any of the preceding current sensors or current measurement coils. A first capacitor 1002 is coupled between the first end 206 of the first measurement coil 202 and ground or a reference voltage. A second capacitor 1004 is coupled between the first end 206 of the first measurement coil 202 and the first end 208 of the second measurement coil 204. A third capacitor 1006 is coupled between the first end 208 of the second measurement coil 204 and ground or a reference voltage. The first 1002, second 1004 and third 1006 capacitors may be provided on the substrate 302 of the current sensor, adjacent to the measurement coils. The capacitors act to provide both common mode and differential filtering, removing high frequency signals which may be large due to the induced coil voltage of the measurement coils being proportional to frequency.

[0158] The capacitors of Figure 10 are particularly useful for the measurement coils described previously. The measurement coils produce a large common mode signal proportional to frequency due to the large circumferential loop formed by the circumferential progression conductors in the advancement region. Which may be a significant antenna for RF signals. The capacitors 1002 and 1006 coupled between the first measurement coil 202 and the second measurement coil 204 and ground acts to provide a low impedance at high frequencies to shunt this common mode signal away. Capacitor 1004 acts to filter away any differential signal that is a residual from mismatch in coupling or components. The coil provides resistance and inductance to create a filter with these components. Other filter approaches are possible.

[0159] The capacitor 1004 coupled between the first measurement coil 202 and the second measurement coil 204 acts to provide filtering of the differential signal, ensuring that despite the proportional to frequency aspect of the induced differential noise signal, at frequencies above the cut-off frequency of the capacitor in combination with the resistance of the coils, the differential mode gain does not continue to increase.

[0160] The current sensor described throughout the description may be coupled to or form part of a larger processing system.

[0161] Figure 11 shows the current sensor including the first current measurement coil 202 and second current measurement coil 204 coupled to a system 1102. The first output terminal 216 and the second output terminal 218 are coupled to differential inputs 1104, 1106 of the processing system 1102. System 1102 may comprise processing circuitry configured to receive the output of the current sensor and determine a current measured by the current measurement coils (the current under test that is passing through the current carrying conductor). As current measurement coils measure a rate of change of current, di / dt, the system may comprise an integrator configured to integrate the outputs of the current measurement coils, such as a low pass filter. System 1102 may further comprise a differential amplifier. The differential amplifier may act to amplify the outputs of the current measurement coils 202, 204 as well as remove any common mode noise coupled into the current measurement coils. System 1002 may additionally or alternatively comprise an analog to digital converter (ADC) coupled to the outputs of the current measurement coils 202, 204.

[0162] As well as providing current measurement, processing system 1102 may act as utility meter or power meter. Processing system 1102 may receive a voltage measurement signal 1102 and determine the power or energy consumption based on the received voltage and determined current. The voltage measurement may be provided by any suitable sensor, such as a shunt resistor. The processing system may additionally or alternatively act as or comprise a circuit breaker system.

[0163] 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.

[0164] Aspects

[0165] A first set of numbered aspects are provided below:

[0166] 1. A current sensor formed on a substrate, the current sensor comprising: a first measurement coil provided on a first layer and a third layer of the substrate; and a second measurement coil, the second measurement coil provided on a second layer and a fourth layer of the substrate.

[0167] 2. The current sensor according to aspect 1, wherein the first layer, the second layer, the third layer and the fourth layer are provided in that order on the substrate.

[0168] 3. The current sensor according to aspect 1 or aspect 2, wherein a distance between the first layer and the second layer is less than a distance between the second layer and the third layer; and wherein a distance between the third layer and the fourth layer is less than the distance between the second layer and the third layer.

[0169] 4. The current sensor according to any preceding aspect, wherein the substrate 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 first measurement coil comprises the first plurality of measurement conductors and the third plurality of measurement conductors, and wherein the second measurement coil comprises the second plurality of measurement conductors and the fourth plurality of measurement conductors.

[0170] 5. The current sensor according to aspect 4, wherein the substrate comprises a first plurality of vias arranged around an inner circumference of the first coil, a second plurality of vias arranged around an inner circumference of the second coil, a third plurality of vias arranged around an outer circumference of the first coil and a fourth plurality of vias arranged around the outer circumference of the second coil.

[0171] 6. The current sensor according to aspect 5, wherein: the first plurality of measurement conductors and the third plurality of measurement conductors are coupled by respective vias of the first plurality of vias and the third plurality of vias, so as to form the first measurement coil; and the second plurality of measurement conductors and the fourth plurality of measurement conductors are coupled by respective vias of the second plurality of vias and the fourth plurality of vias, so as to form the second measurement coil.

[0172] 7. The current sensor according to aspect 6, wherein: the measurement conductors extend radially from a centre of the current sensor; and the substrate further comprises a plurality of circumferential advancement conductors arranged to provide a circumferential progression of the first measurement coil and the second measurement coil.

[0173] 8. The current sensor according to aspect 7, wherein the circumferential advancement conductors are arranged according to at least one of the following : adjacent to the first and second plurality of vias; adjacent to the third and fourth plurality of vias; at a location between the first and second plurality of vias, and the third and fourth plurality of vias.

[0174] 9. The current sensor according to any of aspects 1-6, wherein the measurement conductors are arranged at an angle to a radial direction of the first measurement coil and second measurement coil, such that the measurement conductors provide radial and circumferential progression around the substrate.

[0175] 10. The current sensor according to any preceding aspect, wherein the substrate comprises a path for a current carrying conductor, and wherein the first measurement coil and the second measurement coil are arranged circumferentially around the path. 11. The current sensor according to any preceding aspect, wherein : the first measurement coil has a first end and a second end; the second measurement coil has a first end and a second end.

[0176] 12. The current sensor according to aspect 11, wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops.

[0177] 13. The current sensor according to aspect 12, wherein the first measurement coil and the second measurement coil are arranged relative to each other such that a respective loop of the first plurality of loops is adjacent to a respective loop of the second plurality of loops in a circumferential direction around the path for the current carrying conductor.

[0178] 14. The current sensor according to aspect 11, wherein: each loop of the first plurality of loops of the first measurement coil turn in a clockwise direction from the first end of the first measurement coil; and each loop of the plurality of loops of the second measurement coil turn in a counterclockwise direction from the first end of the second measurement coil

[0179] 15. The current sensor according to any of aspects 11-14, wherein the second end of the first measurement coil is coupled to the second end of the second measurement coil, and configured to be coupled to a reference voltage.

[0180] 16. The current sensor according to any of aspects 11-15, wherein the first end of the first measurement coil and the first end of the second measurement coil are for configured for coupling to a differential signal processing circuit.

[0181] 17. A current sensor comprising: a substrate comprising a path for a conductor for carrying current; a first measurement coil formed on the substrate and arranged to circumferentially progress around the path for the conductor for carrying current, wherein the first measurement coil comprises a first plurality of loops; a second measurement coil arranged to circumferentially progress around the path for the conductor for carrying current, wherein the second measurement coil comprises a second plurality of loops; wherein the first measurement coil and the second measurement coil are arranged relative to each other such that a respective loop of the first plurality of loops is adjacent to a respective loop of the second plurality of loops in a circumferential direction around the path for the conductor for carrying current.

[0182] 18. The current sensor according to aspect 17, wherein each respective loop of the first plurality of loops is not aligned with each respective loop of the second plurality of loops in a direction perpendicular to the substrate.

[0183] 19. The current sensor according to aspect 17 or aspect 18, wherein: the first measurement coil has a first end and a second end; and the second measurement coil has a first end and a second end.

[0184] 20. The current sensor according to aspect 19, wherein: each loop of the plurality of loops of the first measurement coil turn in a clockwise direction from the first end of the first measurement coil; and each loop of the plurality of loops of the second measurement coil turn in a counterclockwise direction from the first end of the second measurement coil; and

[0185] 21. The current sensor of aspect 19 or 20, wherein the second end of the first measurement coil is coupled to the second end of the second measurement coil, and configured to be coupled to a reference voltage.

[0186] 22. The current sensor of any of aspects 19 to 21, wherein the first end of the first measurement coil and the first end of the second measurement coil are for coupling to a signal processing circuit.

[0187] 23. The current sensor according to any of aspects 17-22, wherein the first measurement coil comprises a first plurality of measurement conductors formed on the substrate so as to extend radially from the path for the conductor for carrying current, and wherein the second measurement coil comprises a second plurality of measurement conductors formed on the substrate so as to extend radially from the path for the conductor for carrying current.

[0188] 24. The current sensor according to aspect 23, wherein the first plurality of measurement conductors and the second plurality of measurement conductors do not overlap in a direction perpendicular to a surface of the substrate.

[0189] 25. A current sensor, the current sensor comprising : a first measurement coil having a first end and a second end; a second measurement coil having a first end and a second end; wherein the second end of the first measurement coil is coupled to the second end of the second measurement coil, and configured to be coupled to a reference voltage.

[0190] 26. The current sensor according to aspect 25, wherein: the first end of the first measurement coil is coupled to a first output terminal of the current sensor; and the first end of second measurement coil is configured to be coupled to a second output terminal of the current sensor.

[0191] 27. The current sensor of aspect 26, wherein the first output terminal and the second output terminal are for coupling to a differential signal processing circuit.

[0192] 28. The current sensor according to any of aspects 25-27, wherein the second end of the first measurement coil and the second end of the second measurement coil are coupled to a reference terminal of the current sensor.

[0193] 29. The current sensor according to aspect 28, wherein the reference terminal is for coupling to a reference voltage source.

[0194] 30. The current sensor according to any of aspects 25-29, comprising : a first capacitor coupled between the first end of the first measurement coil and ground; a second capacitor coupled between the first end of the first measurement coil and the first end of the second measurement coil; and a third capacitor coupled between the first end of the second measurement coil and ground.

[0195] 31. The current sensor according to any of aspects 25-30, wherein the current sensor further comprises a path for a conductor for carrying current, the path being positioned in the centre of the first measurement coil and the second measurement coil.

[0196] A second set of numbered aspects are provided below:

[0197] 1. A current sensor, the current sensor comprising : a substrate comprising a first layer, a second layer, a third layer and a fourth layer; a first measurement coil formed on the first layer and the third layer of the substrate; and a second measurement coil, the second measurement coil formed on the second layer and the fourth layer of the substrate.

[0198] 2. The current sensor according to aspect 1, wherein the second layer is positioned between the first layer and the third layer, and wherein the third layer is positioned between the second layer and the fourth layer.

[0199] 3. The current sensor according to aspect 1 or aspect 2, wherein a distance between the first layer and the second layer is less than a distance between the second layer and the third layer; and wherein a distance between the third layer and the fourth layer is less than the distance between the second layer and the third layer.

[0200] 4. The current sensor according to any preceding aspect, wherein the substrate 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 first measurement coil comprises the first plurality of measurement conductors and the third plurality of measurement conductors, and wherein the second measurement coil comprises the second plurality of measurement conductors and the fourth plurality of measurement conductors.

[0201] 5. The current sensor according to aspect 4, wherein the current sensor comprises: a first plurality of vias, formed in the substrate, arranged around an inner circumference of the first coil; a second plurality of vias, formed in the substrate, arranged around an inner circumference of the second coil; a third plurality of vias, formed in the substrate, arranged around an outer circumference of the first coil and a fourth plurality of vias, formed in the substrate, arranged around the outer circumference of the second coil.

[0202] 6. The current sensor according to aspect 5, wherein: the first plurality of measurement conductors and the third plurality of measurement conductors are coupled by respective vias of the first plurality of vias and the third plurality of vias, so as to form the first measurement coil; and the second plurality of measurement conductors and the fourth plurality of measurement conductors are coupled by respective vias of the second plurality of vias and the fourth plurality of vias, so as to form the second measurement coil.

[0203] 7. The current sensor according to aspect 6, wherein: the measurement conductors extend substantially radially from a centre of the current sensor; and the current sensor further comprises a plurality of circumferential progression conductors, formed on the substrate, arranged to provide a circumferential progression of the first measurement coil and the second measurement coil.

[0204] 8. The current sensor according to aspect 7, wherein the circumferential progression conductors are positioned on the substrate to be: adjacent to the first and second plurality of vias; or adjacent to the third and fourth plurality of vias; or at a location between the first and second plurality of vias, and the third and fourth plurality of vias.

[0205] 9. The current sensor according to any of aspects 1-6, wherein the measurement conductors are arranged at an angle to a radial direction of the first measurement coil and second measurement coil, such that the measurement conductors provide radial and circumferential progression around the substrate.

[0206] 10. The current sensor according to any preceding aspect, wherein the substrate comprises a path for a current carrying conductor, and wherein the first measurement coil and the second measurement coil are arranged circumferentially around the path.

[0207] 11. The current sensor according to any preceding aspect, wherein : the first measurement coil has a first end and a second end; and the second measurement coil has a first end and a second end.

[0208] 12. The current sensor according to aspect 11, wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops.

[0209] 13. The current sensor according to aspect 11, wherein the first measurement coil and the second measurement coil are formed on the substrate such that the first plurality of loops of the first measurement coil are interleaved in a circumferential direction with the second plurality of loops of the second measurement coil.

[0210] 14. The current sensor according to aspect 12, wherein the first measurement coil and the second measurement coil are arranged relative to each other such that a respective loop of the first plurality of loops is adjacent to a respective loop of the second plurality of loops in a circumferential direction around the path for the current carrying conductor.

[0211] 15. The current sensor according to aspect 12, wherein: each loop of the first plurality of loops of the first measurement coil turn in a clockwise direction from the first end of the first measurement coil; and each loop of the second plurality of loops of the second measurement coil turn in a counterclockwise direction from the first end of the second measurement coil.

[0212] 16. The current sensor according to any of aspects 11-15, wherein: the second end of the first measurement coil is coupled to the second end of the second measurement coil, and is suitable for coupling to a reference voltage; and the first end of the first measurement coil and the first end of the second measurement coil are suitable for coupling to a differential signal processing circuit.

[0213] 17. A current sensor comprising: a substrate comprising a path for a conductor for carrying current; a first measurement coil formed on the substrate and arranged to circumferentially progress around the path for the conductor for carrying current, wherein the first measurement coil comprises a first plurality of loops; and a second measurement coil formed on the substrate and arranged to circumferentially progress around the path for the conductor for carrying current, wherein the second measurement coil comprises a second plurality of loops; wherein the first measurement coil and the second measurement coil are arranged relative to each other such that a respective loop of the first plurality of loops is adjacent to a respective loop of the second plurality of loops in a circumferential direction around the path for the conductor for carrying current.

[0214] 18. The current sensor according to aspect 17, wherein each respective loop of the first plurality of loops is not aligned with each respective loop of the second plurality of loops in a direction perpendicular to the substrate.

[0215] 19. The current sensor according to aspect 17 or aspect 18, wherein: the first measurement coil has a first end and a second end and each loop of the plurality of loops of the first measurement coil turns in a clockwise direction from the first end of the first measurement coil; and the second measurement coil has a first end and a second end and each loop of the plurality of loops of the second measurement coil turns in a counterclockwise direction from the first end of the second measurement coil. 20. The current sensor of aspect 19, wherein the second end of the first measurement coil is coupled to the second end of the second measurement coil, and configured to be coupled to a reference voltage.

[0216] 21. The current sensor of any of aspects 19 to 20, wherein the first end of the first measurement coil and the first end of the second measurement coil are for coupling to a signal processing circuit.

[0217] 22. The current sensor according to any of aspects 17-21, wherein the first measurement coil comprises a first plurality of measurement conductors formed on the substrate so as to extend radially from the path for the conductor for carrying current, and wherein the second measurement coil comprises a second plurality of measurement conductors formed on the substrate so as to extend radially from the path for the conductor for carrying current.

[0218] 23. The current sensor according to aspect 22, wherein the first plurality of measurement conductors and the second plurality of measurement conductors do not overlap in a direction perpendicular to a surface of the substrate.

[0219] 24. A current sensor, the current sensor comprising : a first output terminal; a second output terminal; a first measurement coil having a first end and a second end, the first end of the first measurement coil coupled to the first output terminal; a second measurement coil having a first end and a second end, the first end of the second measurement coil coupled to the second output terminal; wherein the second end of the first measurement coil is coupled to the second end of the second measurement coil and configured to be suitable for coupling to a reference voltage.

[0220] 25. The current sensor of aspect 24, wherein: the first output terminal and the second output terminal are for coupling to a differential signal processing circuit; and the second end of the first measurement coil and the second end of the second measurement coil are coupled to a reference terminal of the current sensor, wherein the reference terminal is for coupling to a reference voltage source.

[0221] 26. A current measurement system, the current measurement system comprising : the current sensor according to any preceding aspect; and a processing circuit coupled to the current sensor and configured to determine a current under test.

[0222] 27. The current sensor according to any of aspects 25-26, comprising : a first capacitor coupled between the first end of the first measurement coil and ground; a second capacitor coupled between the first end of the first measurement coil and the first end of the second measurement coil; and a third capacitor coupled between the first end of the second measurement coil and ground.

[0223] 28. The current sensor according to any of aspects 25-27, wherein the current sensor further comprises a path for a conductor for carrying current, the path being positioned in the centre of the first measurement coil and the second measurement coil.

[0224] 29. A current sensor, the current sensor comprising : a substrate comprising four layers; a first measurement coil formed on the four layers of the substrate, the first measurement coil comprising a first plurality of turns and a second plurality of turns, wherein the first plurality of turns of the first measurement coil are formed on two of the four layers of the substrate, and the second plurality of turns of the first measurement coil are formed on the other two of the four layers of the substrate.

[0225] 30. The current sensor according to aspect 29, further comprising : a second measurement coil formed on the four layers of the substrate, the second measurement coil comprising a first plurality of turns and a second plurality of turns, wherein the first plurality of turns of the second measurement coil are formed on two of the four layers of the substrate, and the second plurality of turns of the second measurement coil are formed on the other two of the four layers of the substrate.

[0226] 31. The current sensor according to aspect 29 or 30, wherein the first plurality of turns of the first measurement coil comprises the same number of turns as the second plurality of turns of the first measurement coil.

[0227] 32. The current sensor according to any of aspects 29-31, wherein the first plurality of turns of the first measurement coil are formed across a first layer and a third layer of the substrate and the second plurality of turns of the first measurement coil are formed across a second layer and a fourth layer of the substrate.

[0228] 33. The current sensor according to any of aspects 29-31, wherein the first plurality of turns of the first measurement coil are formed across a first layer and a fourth layer of the substrate and the second plurality of turns of the first measurement coil are formed across a second layer and a third layer of the substrate.

[0229] 34. The current sensor according to any of aspects 29-33, wherein the first plurality of turns of the first measurement coil and the second plurality of turns of the first measurement coil are arranged in an interleaved manner.

[0230] 35. The current sensor according to aspect 34, wherein each turn of the first plurality of turns of the first measurement coil is followed, in a circumferential direction, by a turn of the second plurality of turns of the first measurement coil.

[0231] 36. The current sensor according to aspect 34, wherein one or more turns of the first plurality of turns of the first measurement coil are followed by one or more turns of the second plurality of turns of the first measurement coil.

[0232] 37. The current sensor according to aspect 35, wherein a pattern formed by the first plurality of turns of the first measurement coil and the second plurality of turns of the first measurement coil is repeated in a circumferential direction around the first measurement coil.

[0233] 38. A current sensor, the current sensor comprising : a path for a conductor; a first substrate; a first portion of a first measurement coil formed on the first substrate; a first portion of a second measurement coil formed on the first substrate; a second substrate; a second portion of the first measurement coil formed on the second substrate; and a second portion of the second measurement coil formed on the second substrate.

[0234] 39. The current sensor according to aspect 38, wherein: the first portion of the first measurement coil has a first end and a second end; and the first portion of the second measurement coil has a first end and a second end; the second portion of the first measurement coil has a first end and a second end; and the second portion of the second measurement coil has a first end and a second end.

[0235] 40. The current sensor according to aspect 38 or 39, wherein: a combination of the first portion of the first measurement coil and the second portion of the first measurement coil progresses so as to substantially surround the path for the conductor in a circumferential direction; a combination of the first portion of the second measurement coil and the second portion of the second measurement coil progresses so as to substantially surround the path for the conductor in the circumferential direction.

[0236] 41. The current sensor according to any of aspects 38-40, wherein: the first portion of the first measurement coil and the first portion of the second measurement coil progress 180 degrees around the path for the conductor; and the second portion of the first measurement coil and the second portion of the second measurement coil progress 180 degrees around the path for the conductor.

[0237] 42. The current sensor according to any of aspects 38-40, wherein: the first portion of the first measurement coil and the first portion of the second measurement coil progress 270 degrees around the path for the conductor; and the second portion of the first measurement coil and the second portion of the second measurement coil progress 90 degrees around the path for the conductor.

[0238] 43. The current sensor according to any of aspects 38-42, wherein the second substrate comprises a processing circuit coupled to the second portion of the first measurement coil and the second portion of the second measurement coil.

[0239] 44. The current sensor according to any of aspects 38-43, wherein the first substrate and the second substrate are coupled to one another using a hinge.

Claims

Claims1. A current sensor, the current sensor comprising : a substrate comprising a first layer, a second layer, a third layer and a fourth layer; a first measurement coil formed on the first layer and the third layer of the substrate; and a second measurement coil, the second measurement coil formed on the second layer and the fourth layer of the substrate.

2. The current sensor according to claim 1, wherein the second layer is positioned between the first layer and the third layer, and wherein the third layer is positioned between the second layer and the fourth layer.

3. The current sensor according to claim 1 or claim 2, wherein a distance between the first layer and the second layer is less than a distance between the second layer and the third layer; and wherein a distance between the third layer and the fourth layer is less than the distance between the second layer and the third layer.

4. The current sensor according to any preceding claim, wherein the substrate 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 first measurement coil comprises the first plurality of measurement conductors and the third plurality of measurement conductors, and wherein the second measurement coil comprises the second plurality of measurement conductors and the fourth plurality of measurement conductors.

5. The current sensor according to claim 4, wherein the current sensor comprises: a first plurality of vias, formed in the substrate, arranged around an inner circumference of the first coil; a second plurality of vias, formed in the substrate, arranged around an inner circumference of the second coil; a third plurality of vias, formed in the substrate, arranged around an outer circumference of the first coil and a fourth plurality of vias, formed in the substrate, arranged around the outer circumference of the second coil.

6. The current sensor according to claim 5, wherein: the first plurality of measurement conductors and the third plurality of measurement conductors are coupled by respective vias of the first plurality of vias and the third plurality of vias, so as to form the first measurement coil; and the second plurality of measurement conductors and the fourth plurality of measurement conductors are coupled by respective vias of the second plurality of vias and the fourth plurality of vias, so as to form the second measurement coil.

7. The current sensor according to claim 6, wherein: the measurement conductors extend substantially radially from a centre of the current sensor; and the current sensor further comprises a plurality of circumferential progression conductors, formed on the substrate, arranged to provide a circumferential progression of the first measurement coil and the second measurement coil.

8. The current sensor according to claim 7, wherein the circumferential progression conductors are positioned on the substrate to be: adjacent to the first and second plurality of vias; or adjacent to the third and fourth plurality of vias; or at a location between the first and second plurality of vias, and the third and fourth plurality of vias.

9. The current sensor according to any of claims 1-6, wherein the measurement conductors are arranged at an angle to a radial direction of the first measurement coil and second measurement coil, such that the measurement conductors provide radial and circumferential progression around the substrate.

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

11. The current sensor according to claim 10, wherein the first measurement coil comprises a first plurality of loops and the second measurement coil comprises a second plurality of loops.

12. The current sensor according to claim 11, wherein the first measurement coil and the second measurement coil are formed on the substrate such that the first plurality of loops of the first measurement coil are interleaved in a circumferential direction with the second plurality of loops of the second measurement coil.

13. The current sensor according to claim 11 or claim 12, wherein: each loop of the first plurality of loops of the first measurement coil turn in a clockwise direction from the first end of the first measurement coil; and each loop of the second plurality of loops of the second measurement coil turn in a counterclockwise direction from the first end of the second measurement coil.

14. The current sensor according to any of claims 11-13, wherein: the second end of the first measurement coil is coupled to the second end of the second measurement coil, and is suitable for coupling to a reference voltage; and the first end of the first measurement coil and the first end of the second measurement coil are suitable for coupling to a differential signal processing circuit.

15. A current sensor comprising: a substrate comprising a path for a conductor for carrying current; a first measurement coil formed on the substrate and arranged to circumferentially progress around the path for the conductor for carrying current, wherein the first measurement coil comprises a first plurality of loops; and a second measurement coil formed on the substrate and arranged to circumferentially progress around the path for the conductor for carrying current, wherein the second measurement coil comprises a second plurality of loops; wherein the first measurement coil and the second measurement coil are arranged relative to each other such that a respective loop of the first plurality of loops is adjacent to a respective loop of the second plurality of loops in a circumferential direction around the path for the conductor for carrying current.

16. The current sensor according to claim 15, wherein each respective loop of the first plurality of loops is not aligned with each respective loop of the second plurality of loops in a direction perpendicular to the substrate.

17. The current sensor according to claim 15 or claim 16, wherein: the first measurement coil has a first end and a second end and each loop of the plurality of loops of the first measurement coil turns in a clockwise direction from the first end of the first measurement coil; and the second measurement coil has a first end and a second end and each loop of the plurality of loops of the second measurement coil turns in a counterclockwise direction from the first end of the second measurement coil.

18. A current sensor, the current sensor comprising : a first output terminal; a second output terminal;a first measurement coil having a first end and a second end, the first end of the first measurement coil coupled to the first output terminal; a second measurement coil having a first end and a second end, the first end of the second measurement coil coupled to the second output terminal; wherein the second end of the first measurement coil is coupled to the second end of the second measurement coil and configured to be suitable for coupling to a reference voltage.

19. The current sensor of claim 18, wherein: the first output terminal and the second output terminal are for coupling to a differential signal processing circuit; and the second end of the first measurement coil and the second end of the second measurement coil are coupled to a reference terminal of the current sensor, wherein the reference terminal is for coupling to a reference voltage source.

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