Current transducer with TMR magnetic field sensor

Abstract

The invention relates to a current transducer with a TMR magnetic field sensor. A current transducer (100) comprising a housing (104), a secondary conductor arrangement (114) and a magnetic field sensor (2) connected to the secondary conductor arrangement, the magnetic field sensor (2) comprising at least a first tunnel magnetoresistance (TMR) sensor (2a), the TMR sensor comprising a die substrate (4), a Wheatstone bridge circuit (10) arranged on the die substrate, and supply and measurement output connection terminals (14) arranged on the die substrate, a Wheatstone bridge circuit for connecting a Wheatstone bridge circuit to an external circuit via a secondary conductor arrangement for power supply and measurement signal processing, the Wheatstone bridge circuit comprising four circuit branches (12), each circuit branch interconnecting a supply terminal to a measurement output terminal and comprising a respective TMR resistor. Each TMR resistor comprises a first TMR half-resistor and a second TMR half-resistor, the first and second TMR half-resistors being arranged in radially opposite quadrants (6) of the die substrate.

Description

Technical Field

[0001] The present invention relates to a current transducer having a tunneling magnetoresistance (TMR) magnetic field sensor. Background Art

[0002] Current transducers with TMR magnetic field sensors are known, where the TMR magnetic field sensor is configured to measure the magnetic field generated by a primary conductor located near the in-plane magnetic field sensor. The primary conductor typically may have a U-shaped portion with parallel first and second branches connected together at one end by a bridging portion. In this case, the gradient sensor typically may have a first sensing element adjacent and overlapping one of the primary conductor branches and a second sensing element adjacent and overlapping the other primary conductor branch. Currents in the first and second branches flow in opposite directions, thus generating a magnetic field gradient in a direction transverse to the first and second branches and thus can be picked up by the TMR magnetic field sensor.

[0003] Some TMR-based sensors include four TMR resistors arranged in a Wheatstone bridge circuit (usually also referred to as a full bridge), with each resistor of the Wheatstone bridge consisting of one TMR resistor.

[0004] In an environment subjected to thermal gradients, mechanical stress, or magnetic field gradients, the spaced layout of the TMR resistors on the TMR sensor substrate affects the TMR resistors to varying degrees depending on their position on the substrate, resulting in measurement errors. In addition, in a current transducer having a pair of TMR magnetic field sensors, the measurement errors are more prominent because the current measurement is based on the outputs of two TMR sensors, each of which contains measurement errors.

[0005] If the TMR sensors are well-calibrated and balanced, they are very precise. However, imbalances caused by external factors affecting the resistors of the Wheatstone bridge in different ways result in unacceptable measurement errors that are not easily compensated. Summary of the Invention

[0006] In view of the above, an object of the present invention is to provide a current transducer having a TMR magnetic field sensor that is accurate and reliable even in the presence of gradients of magnetic fields, temperature, or stress that affect the response of the TMR sensor.

[0007] It is advantageous to provide a compact current transducer.

[0008] It is advantageous to provide a cost-effective current transducer in terms of manufacturing.

[0009] It is advantageous to provide a current transducer that is easy to interconnect and control with an external circuit.

[0010] The object of the present invention is achieved by providing a current transducer having a TMR magnetic field sensor according to claim 1. The dependent claims set forth various advantageous embodiments.

[0011] The present application discloses a current transducer, comprising a housing, a secondary conductor arrangement, and a magnetic field sensor connected to the secondary conductor arrangement. The magnetic field sensor includes at least a first tunnel magnetoresistance (TMR) sensor. The TMR sensor includes a die substrate, a Wheatstone bridge circuit arranged on the die substrate, and supply and measurement output connection terminals arranged on the die substrate for connecting the Wheatstone bridge circuit to an external circuit via the secondary conductor arrangement for power supply and measurement signal processing. The Wheatstone bridge circuit includes four circuit branches, each circuit branch interconnecting the supply terminal to the measurement output terminal and including a corresponding TMR resistor.

[0012] According to one aspect of the present invention, each TMR resistor includes a first TMR half-resistor and a second TMR half-resistor, and the first and second TMR half-resistors are arranged in diametrically opposed quadrants of the die substrate.

[0013] In an advantageous embodiment, the magnetic field sensor includes a second TMR sensor arranged in a spaced-apart relationship with the first TMR sensor, which is configured to measure the magnetic field gradient.

[0014] In an advantageous embodiment, the current transducer further includes a primary conductor, which includes a first connection terminal and a second connection terminal.

[0015] In an advantageous embodiment, the primary conductor includes an intermediate portion interconnecting the first connection terminal and the second connection terminal. The intermediate portion has a first branch, a second branch, and a bridging branch interconnecting one end of the first branch and one end of the second branch. The first and second branches are separated by a gap.

[0016] In an advantageous embodiment, the primary conductor includes an intermediate portion interconnecting the first connection terminal and the second connection terminal. The intermediate portion has a reduced cross-sectional area compared to the first connection terminal and the second connection terminal, and the first connection terminal and the second connection terminal are separated by a gap.

[0017] In an advantageous embodiment, the magnetic field gradient sensor is mounted on the surface of the primary conductor, and the surface of the primary conductor is separated from the magnetic field gradient sensor by an insulating layer.

[0018] In an advantageous embodiment, except for the connection terminals of the primary conductor and the secondary conductor arrangement, the primary conductor, the secondary conductor arrangement, and the magnetic field gradient sensor are overmolded with an insulating housing.

[0019] In an advantageous embodiment, the primary conductor and the secondary conductor arrangement are formed by a lead frame.

[0020] In an advantageous embodiment, each TMR resistor comprises a plurality of TMR elements which are connected in series in part by conductive interconnect tracks.

[0021] In an advantageous embodiment, the number of TMR elements of each TMR half resistor is greater than one hundred.

[0022] In an advantageous embodiment, the interconnect track part is arranged on at least a first layer and a second layer of the substrate, and the TMR elements form an interconnection between the first layer and the second layer.

[0023] In an advantageous embodiment, each TMR resistor part comprises a pinned ferromagnetic layer mounted on the first layer of the substrate and a free ferromagnetic layer mounted on the second layer of the substrate.

[0024] In an advantageous embodiment, the TMR elements of the plurality of TMR elements are spaced apart from adjacent serially connected TMR elements at substantially equal distances.

[0025] In an advantageous embodiment, the TMR elements of each TMR half resistor are arranged at positions extending from the central region of the die substrate to a position close to the outer boundary of the die substrate.

[0026] In an advantageous embodiment, the corresponding TMR sensor terminals comprise a pair of the output terminals and a pair of the supply terminals, each terminal being arranged at the outer corners of the four quadrants. Description of the Drawings

[0027] Other objects and advantageous features of the present invention will become apparent from the claims, the detailed description and the drawings, wherein:

[0028] Figure 1a is a perspective view of a current transducer according to an embodiment of the present invention;

[0029] Figure 1b is a perspective view of a current transducer according to another embodiment of the present invention;

[0030] Figure 2 is a schematic circuit diagram of a TMR full-bridge magnetic field sensor according to the prior art;

[0031] Figures 2a and 2b are schematic circuit diagrams of possible arrangements of TMR resistors for explaining problems related to non-centroid arrangements;

[0032] Figures 3a and 3b are further exemplary layouts of non-centroid arrangements of similarly TMR resistors for explaining problems of non-centroid arrangements;

[0033] Figure 4Schematic circuit diagram of the TMR magnetic field sensor of the current transducer according to an embodiment of the present invention;

[0034] Figure 5a and Figure 5b Simplified schematic diagram of the layout of the TMR resistor of the TMR magnetic field sensor according to an embodiment of the present invention;

[0035] Figure 6a and Figure 6b similar to Figure 5a and Figure 5b variant;

[0036] Figure 7a Schematic top view of the TMR magnetic field sensor of the current transducer according to an embodiment of the present invention, but it should be noted that the TMR resistor and the interconnects are not drawn to scale and are enlarged and simplified to illustrate the concept, since the sub - micron scale of the TMR resistor elements and the interconnects can vary over a wide range between more than one hundred to several thousand, showing the actual design to scale would impede visibility;

[0037] Figure 7b is Figure 7a perspective view of an embodiment of;

[0038] Figure 7c is Figure 7b detailed partial view of the central part of an embodiment of. Detailed Description

[0039] Referring to the accompanying drawings, a current transducer 100 according to an embodiment of the present invention includes a magnetic field gradient sensor 2, a secondary conductor arrangement 114, and a housing 104 that surrounds or encapsulates a part of the magnetic field gradient sensor and the secondary conductor arrangement. The housing 104 may include overmolding, as is well known per se in the field of current transducers.

[0040] In an advantageous embodiment, the current transducer may include a primary conductor 105, and the housing 104 partially surrounds or encapsulates the primary conductor, exposing contact terminals for connection to an external circuit.

[0041] In other embodiments, the current transducer may be arranged such that no primary conductor is incorporated and is configured to be mounted near an external primary conductor. For example, the primary conductor 105 may be provided on or inside a circuit board of an external circuit, and the current transducer is mounted and connected to the circuit board.

[0042] The current transducer may also optionally include a signal conditioning chip 103 electrically connected to the magnetic field gradient sensor 2, and the signal conditioning chip 103 may include an electrostatic discharge (ESD) protection diode and / or a temperature sensor in the form of a temperature diode. In one variant (not shown), the signal conditioning chip may be omitted, and the magnetic field gradient sensor may be directly connected to the secondary conductor arrangement.

[0043] The magnetic field gradient sensor includes at least one TMR sensor connected, for example, via bonding wires to the signal conditioning chip or the secondary conductor arrangement. In a preferred embodiment, the magnetic field gradient sensor includes a pair of spaced-apart TMR sensors.

[0044] The current transducer 100 also includes a secondary conductor arrangement 114 electrically connected to the magnetic field gradient sensor 2, the temperature sensor, and the signal conditioning chip 103 (if present) for power and signal communication with an external circuit. The electrical interconnection between the signal conditioning chip 103, the magnetic field gradient sensor 2, and the secondary conductor arrangement 114 can be achieved by various interconnections 116 known per se, such as bonding wires or solder balls in flip-chip interconnections. In a preferred embodiment, the interconnection 116 between the chip and the secondary conductor arrangement is performed with bonding wires such that the signal conditioning chip 103 can be positioned closer to the primary conductor 105 and farther from the secondary conductor arrangement 114.

[0045] The primary conductor 105 and the secondary connector arrangement 114 can be stamped from a lead frame, in other words, cut out from a strip of metal sheet as is well known per se in the field of current transducers.

[0046] In the illustrated embodiment, the secondary conductor arrangement 114 has connection terminals provided with surface-mount pads exposed on the mounting side 118 of the housing 104. The primary conductor 105 has first and second connection end terminals 110a, 110b, which can advantageously be in the form of surface-mount connection pads and are configured for surface-mount connection of the current transducer on an external circuit board. Such a surface-mount connection structure is also well known in the field of current transducers. However, the primary conductor and the secondary conductor arrangement may have connection terminals with other forms and structures for connection to an external circuit, such as pin contacts, without departing from the scope of the present invention.

[0047] As is well known in the field of current transducers, the primary conductor is configured to be connected to a conductor carrying the current to be measured, and the current to be measured flows through the primary conductor and generates a magnetic field related to the magnitude of the primary current to be measured.

[0048] The magnetic field gradient sensor 2 includes a first TMR sensor 2a and a second TMR sensor 2b, and is configured to measure a magnetic field in a measurement plane that extends through and overlies (or underlies) the first TMR sensor 2a and the second TMR sensor 2b. The measurement plane is a plane parallel to the main surface of the primary conductor 105, which in the illustrated embodiment is parallel to the mounting side 118 of the current transducer.

[0049] In an advantageous embodiment, the primary conductor 105 has a first branch 106a, a second branch 106b, and a bridging branch 108 that interconnects one end of the first branch and one end of the second branch, such that the primary conductor has a substantially U-shaped portion. The ends of the first and second branches opposite the bridging branch 108 are each connected to a connection terminal, the first branch 106a being connected to a first connection terminal 110a and the second branch 106b being connected to a second connection terminal 110b. As previously mentioned, the connection terminals can have the form of, for example, surface-mount pads for surface-mount connection to conductive traces on a circuit board. The width W of each of the first and second connection terminals can advantageously exceed 30% of the total width WT of the current transducer to provide a good electrical connection, especially a thermal connection, to the external circuit board to which the transducer is to be connected.

[0050] In Figure 1a In the illustrated advantageous embodiment, the first TMR sensor 2a is located above (overlapping) the first branch 106a of the primary conductor, while the second TMR sensor 2b is located above (overlapping) the second branch 106b of the primary conductor. The first TMR sensor and the second TMR sensor can be mounted on the upper surface of the primary conductor and separated therefrom by an insulating layer. The insulating layer can be, for example, a polyimide layer or another polymer layer that is typically less than 0.5 mm thick.

[0051] The first TMR sensor 2a and the second TMR sensor 2b are made of a semiconductor chip that has, for example, a silicon substrate on which the TMR sensors are implemented. The first branch 106a and the second branch 106b can extend substantially parallel to each other and are arranged and shaped symmetrically with respect to a centerline C. However, this centerline need not correspond to the centerline extending through the current transducer housing.

[0052] Each branch has an inner edge 122, and the inner edges of the first and second branches face each other and are separated by a gap G.

[0053] In Figure 1bIn another embodiment shown, the primary conductor includes an intermediate portion interconnecting first and second connection end terminals 110a, 110b, the intermediate portion having a reduced cross-sectional area compared to the first and second connection end terminals, and the first and second connection end terminals being separated by a gap (G). In this embodiment, the first TMR sensor 2a may be located above the intermediate portion, while the second TMR sensor 2b may be located at an interval not above the intermediate portion, configured to measure the magnetic field gradient generated by the primary conductor 105.

[0054] Although the primary and secondary conductors have been described as being formed by a lead frame, in a variant, the primary and / or secondary conductors may be formed by other techniques known per se, such as by depositing metal traces on a substrate.

[0055] Referring to the prior art TMR sensor arrangements of FIGS. 2 to 3b, problems associated with a conventional non-centroidal TMR resistor arrangement for a TMR sensor used in a current transducer are explained, which are subject to external effects generating gradients.

[0056] The circuit in FIG. 2 is a full-bridge magnetoresistive sensor. The arrows indicate the direction of magnetization of the pinned or reference layer. In the context of this study, the magnetization of the reference layer is parallel to the x-axis, and the sensitivity of the sensor is also along the x-axis, which means they respond to the x-component (magnetic flux density) of the B-field.

[0057] FIGS. 2a and 2b show a possible layout according to the prior art, where the patches labeled Ri represent the areas of the sensors, on which the TMR elements are connected in series to form the resistors Ri as shown in the circuit of FIG. 2. These elements each have a magnetoresistive response, and in this model, we assume that these resistors have a linearized response, and the behavior of the TMR series array can be approximated by an equivalent lumped TMR located at the centroid of the patch. As an example, these centroids are separated by distances dx and dy, and the coordinates used in the model for patch R1a are (-dx / 2, +dy / 2).

[0058] Modeling the gradients along the x and y axes, and for simplicity, modeling the gradients along the diagonal axes within the u, v coordinate system.

[0059] Temperature and magnetic field are modeled in an approximate manner by fields on x, y or u, v, having uniform common-mode components and coefficients of gradients along the axes:

[0060] In the case of x, y:

[0061] DeltaT(x, y):=ΔT(1+a ,

[0061] ,

[0062] , ,

[0060] , x , y x+a y y)

[0062] Bx(x, y) := B 0x (1 + b x x + b y y)

[0063] In the case of u, v:

[0064] DeltaT(u, v) := ΔT(1 + a u u + a v v)

[0065] Bx(u, v) := B 0x (1 + b u u + b v v)

[0066] Here, temperature is chosen as an example of an influencing quantity that is easy to model. It can represent other influencing quantities to which the sensor will have some unwanted responses. For example, for various components of mechanical stress, a similar influence of potential symmetry can be expected.

[0067] Case 1 - Shifted layout

[0068] Two half - bridges are simply placed adjacent to each other along the X - axis, as shown in Figures 2a and 2b.

[0069] Ideal response - Assuming a uniform B - field along the x - direction and a uniform temperature, a resistance insensitive to temperature and a magnetoresistance insensitive to temperature, the normalized bridge output (independent of the bridge supply voltage) is:

[0070] B 0x S0

[0071] Simply applying the common - mode field B 0x multiplied by the linearized magnetic sensitivity S0

[0072] Effect of magnetic field gradient

[0073] Since these sensors will operate within a gradient sensor, the magnetic field may be non - uniform and have a gradient component that extends over the space occupied by the sensor. This model covers this situation, and the first 3 terms of the polynomial approximation of the sensor response are shown here:

[0074] Magnetic field gradient component b x

[0075]

[0076] Magnetic field gradient component b y

[0077]

[0078] Magnetic field gradient component b u

[0079]

[0080] Magnetic field gradient component b v

[0081]

[0082] Obviously, in the presence of a field gradient, the sensor response becomes non - linear for the higher - order terms in B ox and is also proportional to the gradient * spacing. The most typical case will involve a gradient along the x - direction.

[0083] Effect of temperature gradient on the offset caused by the resistance TCR

[0084] Temperature field gradient component a x 0

[0086] Temperature field gradient component a y 0

[0088] Temperature field gradient component a u

[0089]

[0090] Temperature field gradient component a v

[0091]

[0092] Effect of temperature gradient on the sensor response caused only by the TMR temperature coefficient, third - order polynomial approximation:

[0093] Uniform temperature rise

[0094] (S0TC M ΔT+S0)B 0x +...

[0095] Temperature field gradient component a x

[0096] (S0TC M ΔT+S0)B 0x +...

[0097] Temperature field gradient component a y

[0098]

[0099] Temperature field gradient component a u

[0100]

[0101] Temperature field gradient component a v

[0102]

[0103] Case 2 - Crossed layout

[0104] The two half - bridges cross each other as shown in Figures 3a and 3b.

[0105] Ideal response - assuming a uniform B - field along the x - direction, uniform temperature, temperature - insensitive resistors, and temperature - insensitive magnetoresistors, the normalized bridge output (independent of the bridge supply voltage) is:

[0106] B 0x S0

[0107] Simply apply the common - mode field B 0x Multiply by the linearized magnetic sensitivity S0

[0108] Effect of the magnetic field gradient

[0109] Since these sensors will operate within a gradient sensor, the magnetic field may be non - uniform and have gradient components that extend over the space occupied by the sensor. This model covers such a case, and the first three terms of a polynomial approximation of the sensor response are shown here:

[0110] Magnetic field gradient component b x

[0111]

[0112] Magnetic field gradient component b y

[0113]

[0114] Magnetic field gradient component b u

[0115]

[0116] Magnetic field gradient component b v

[0117]

[0118] Obviously, in the presence of a field gradient, the sensor response becomes non - linear in the higher - order terms of B ox and is also proportional to the gradient * spacing. The most typical case will involve a gradient along the x - direction.

[0119] Effect of the temperature gradient on the offset caused by the resistor TCR

[0120] Temperature field gradient component a x

[0121]

[0122] Temperature field gradient component a y 0

[0124] Temperature field gradient component a u

[0125]

[0126] Temperature field gradient component a v

[0127]

[0128] Effect of temperature gradient on the sensor response caused only by the TMR temperature coefficient, third-order polynomial approximation:

[0129] Uniform temperature rise

[0130] (S0TC M ΔT + S0)B 0x +...

[0131] Temperature field gradient component a x

[0132]

[0133] Temperature field gradient component a y

[0134]

[0135] Temperature field gradient component a u

[0136]

[0137] Temperature field gradient component a v

[0138]

[0139] From two simple layouts of a full-bridge magnetoresistive sensor, it is obvious that they have an undesirable sensitivity to magnetic field gradients, temperature, and other similar influencing quantities such as mechanical stress.

[0140] Now referring to Figures 4 to 7c , embodiments of the present invention will now be described.

[0141] A TMR sensor according to an embodiment of the present invention includes a substrate 4 and a Wheatstone bridge circuit 10 disposed on layers of the substrate. The Wheatstone bridge circuit includes circuit branches 12 and terminals 14. The terminals 14 include output terminals 14a, 14b and supply terminals 14c, 14d, and four circuit branches 12a, 12b, 12c, 12d, which are interconnected with the output terminals and the supply terminals in a Wheatstone bridge arrangement, as is well known per se. The output terminals include a first output terminal V− and a second output terminal V+ that provide a measurement signal Vout of the circuit. The supply terminals 14c, 14d are for connection to a first and a second reference voltage VSS, VDD, such as a reference power supply voltage and a ground connection.

[0142] Each circuit branch includes TMR resistors R1, R2, R3, R4. Each circuit branch resistor is formed by a plurality of TMR elements connected in series. Each TMR element has a pinned ferromagnetic layer and a free ferromagnetic layer separated by an insulating layer. The magnetic orientation of the pinned layer of each TMR element is oriented substantially in the same direction. In other words, the orientation directions of the ferromagnetic layers of the TMR elements of each of the TMR resistors R1, R2, R3, R4 are parallel to each other.

[0143] As is well known per se, when a magnetic field orients the magnetic field of the free layer in the same direction as the pinned layer, the resistance of the TMR element decreases proportionally to the magnitude of the magnetic field. Embodiments may include TMR based on a uniformly magnetized free layer and TMR with a "vortex state" free layer. In the vortex state free layer, the magnetization vector is arranged in a rotational pattern. The operating principles of these embodiments all result in a sensor response to the component of the applied magnetic field in the direction of the pinned layer magnetization.

[0144] According to one aspect of the present invention, each branch resistor R1, R2, R3, R4 includes a first half resistor R1a, R2a, R3a, R4a and a second half resistor R1b, R2b, R3b, R4b, which are arranged around a centroid in radially opposite quadrants 6 of a square surface area. The first and second half resistors have the same characteristics, i.e., they have substantially the same resistance when subjected to a given magnetic field under the same conditions.

[0145] In a preferred embodiment, each of the TMR first and second half-resistors has a plurality of TMR elements 16, which are arranged in a spaced-apart manner within the respective quadrants 6 and are interconnected by the interconnecting portions of conductor tracks 18, 18-1, 18-2 that interconnect the supply terminals to the output terminals. The TMR elements 16 are interconnected in series. The conductor tracks 18 preferably have interconnecting portions 18-1, 18-2 disposed on the first and second layers 4a, 4b of the die substrate 4, whereby the interconnecting portions of different circuit branches cross each other at the central region 19 of the square surface area within which the four quadrants 6a, 6b, 6c, 6d are disposed.

[0146] Each TMR element 16 can be arranged such that the pinned layer is positioned near the first substrate layer 4a and the free layer is positioned near the second substrate layer 4b. However, it should be noted that, without departing from the scope of the present invention, the pinned and free layers of the TMR element can be reversed or can be different in one circuit branch relative to another.

[0147] In an advantageous embodiment, each of the half-resistors Ria, Rib includes a plurality of TMR elements, which can be more than one hundred to several thousand. Figures 7a to 7c The simplified diagrams are not drawn to scale and are intended to illustrate the concept, as showing the actual layout pattern to scale would impede visibility due to the large number of TMR elements and the sub-micron scale. It can be noted that increasing the number of TMR elements increases the resistance, which can be desirable, and reduces the noise, which is highly desirable. The TMR elements 16 are preferably interconnected in a spaced-apart manner, being distributed substantially uniformly across from the center to the corners of the square surface area in order to avoid crosstalk and mutual influence between adjacent TMR elements. This spacing also facilitates the fabrication and magnetization of individual TMR elements. As is well known in the TMR sensor field itself, the TMR insulating layer is preferably of the MgO (magnesium oxide) type. The four terminals or pads forming the measurement and supply terminal pairs are preferably disposed at the corners of the square surface area defining the four quadrants.

[0148] Now let us consider in more detail how the embodiments of the present invention provide better immunity to the amount of gradient influence compared to the prior art discussed previously.

[0149] Embodiments of the present invention – common centroid full-bridge layout.

[0150] The circuit is shown in Figure 4 Each resistor in the full bridge is divided into two equal half-resistors ria and rib.

[0151] Then, four pairs of half-resistors are arranged such that the centroid of each pair of half-resistors coincides with the center of the sensor die, for example as shown in Figure 5a , 5bAs shown, although other shapes will also satisfy this condition. As a result, if such a full bridge is to be implemented on a larger substrate, the coordinates of the centroid of each half-resistor pair will exhibit symmetry with respect to the center of the die or the center of the layout of the full bridge.

[0152] Ideal response: Assuming a uniform magnetic field B in the x direction, a uniform temperature, a temperature-insensitive resistance, and a temperature-insensitive magnetoresistance, the normalized bridge output (independent of the bridge supply voltage) is:

[0153] B 0x S0

[0154] Simply apply the common-mode field B 0x Multiply by the linearized magnetic sensitivity S0

[0155] Effect of magnetic field gradient

[0156] Since these sensors will operate within a gradient sensor, the magnetic field may be non-uniform and have gradient components that extend over the space occupied by the sensors. This model covers such a case, and the first three terms of the polynomial approximation of the sensor response are shown here:

[0157] Magnetic field gradient component b x

[0158] S0B 0x +...

[0159] Magnetic field gradient component b y

[0160] S0B 0x +...

[0161] Magnetic field gradient component b u

[0162] S0B 0x +...

[0163] Magnetic field gradient component b v

[0164] S0B 0x +...

[0165] The polynomial approximation up to the third order does not show non-linearity in the presence of field gradients along the four axes modeled here.

[0166] Effect of temperature gradient on the offset caused by the resistor TCR

[0167] Temperature field gradient component a x 0

[0169] Temperature field gradient component a y 0

[0171] Temperature field gradient component a u 0

[0173] Temperature field gradient component a v 0

[0175] Effect of temperature gradient on sensor response caused only by the TMR temperature coefficient, third-order polynomial approximation:

[0176] Uniform temperature rise

[0177] (S0TC M ΔT + S0)B 0x +...

[0178] Temperature field gradient component a x

[0179] (S0TC M ΔT + S0)B 0x +...

[0180] Temperature field gradient component a y

[0181] (S0TC M ΔT + S0)B 0x +...

[0182] Temperature field gradient component a u

[0183] (S0TC M ΔT + S0)B 0x +...

[0184] Temperature field gradient component a v

[0185] (S0TC M ΔT + S0)B 0x +...

[0186] Due to symmetry, all four resistors of the bridge share a common centroid, so the common-centroid full-bridge layout is insensitive to the quantity being measured and the gradients of the influencing quantities.

[0187] Different arrangements of the common-centroid layout, such as Figure 6a 、 6b shown, can use a model similar to the above to verify that it satisfies the same characteristics.

[0188] In an embodiment of the present invention, the symmetric arrangement of the four resistors of the full bridge includes a plurality of TMR elements connected in series in a cross layout, advantageously using two metallization layers and the TMR elements themselves as vias crossing from one side to the other.

[0189] There are several pinned layer magnetization patterns that are compatible with the series connection layout and the cross layout. The preferred pattern is the one that results in the same magnetization over a large area because this makes the pinned layer selective programming processing steps easier and faster.

[0190] List of reference numerals used

[0191] Current transducer 100

[0192] Magnetic field gradient sensor 2

[0193] TMR sensors 2, 2a, 2b

[0194] Die / substrate 4

[0195] First layer 4a

[0196] Second layer 4b

[0197] Quadrants 6a, 6b, 6c, 6d

[0198] Center

[0199] Corner region 8

[0200] Wheatstone bridge circuit 10

[0201] Circuit branch 12

[0202] First branch circuit 12a

[0203] Second branch circuit 12b

[0204] Third branch circuit 12c

[0205] Fourth branch circuit 12d

[0206] Terminal 14

[0207] Output terminals 14a, 14b

[0208] First output terminal Vout-

[0209] Second output terminal Vout+

[0210] Supply terminals 14c, 14d

[0211] First supply terminal Vss

[0212] Second supply terminal Vdd

[0213] TMR-based resistor R(N): R1, R2, R3, R4

[0214] First branch resistor R1

[0215] Second branch resistor R2

[0216] Third branch resistor R3

[0217] Fourth branch resistor R4

[0218] First half resistor, second half resistor Ria, Rib (i = 1, 2, 3, 4)

[0219] TMR element 16

[0220] Pinned ferromagnetic layer

[0221] Insulating spacer layer

[0222] Free ferromagnetic layer

[0223] Conductor track 18

[0224] Interconnection portion 18-1 on the pinned layer

[0225] Interconnection portion 18-2 on the free layer

[0226] Signal conditioning chip 103

[0227] ESD protection diode, temperature sensor

[0228] Molded housing 104

[0229] Mounting side 118

[0230] Primary conductor 105

[0231] First branch 106a

[0232] Inner edge 122

[0233] Second branch 106b

[0234] Inner edge 122

[0235] Bridging branch 108

[0236] First connection terminal 110a

[0237] Surface mount pad

[0238] Second connection terminal 110b

[0239] Surface mount pad

[0240] Secondary conductor arrangement 114

[0241] Connection terminal

[0242] Surface-mount pad

[0243] Interconnection 116

[0244] Bonding wire

[0245] Center line C

Claims

1. A current transducer (100) comprising a housing (104), a secondary conductor arrangement (114) and a magnetic field sensor (2) connected to the secondary conductor arrangement, the magnetic field sensor (2) comprising at least a first tunnel magnetoresistive TMR sensor (2a), the TMR sensor comprising a die substrate (4), a Wheatstone bridge circuit (10) arranged on the die substrate, and supply and measurement output connection terminals (14) arranged on the die substrate for connecting the Wheatstone bridge circuit to an external circuit via the secondary conductor arrangement for power supply and measurement signal processing, the Wheatstone bridge circuit comprising four circuit branches (12), each circuit branch interconnecting a supply terminal to a measurement output terminal and comprising a respective TMR resistor, characterized in that, Each TMR resistor includes a first TMR half-resistor and a second TMR half-resistor, and the first and second TMR half-resistors are arranged in radially opposite quadrants (6) of the die substrate.

2. The current transducer according to the preceding claim, wherein the magnetic field sensor includes a second TMR sensor (2b), and the second TMR sensor is arranged in a spaced relationship with the first TMR sensor and is configured to measure a magnetic field gradient.

3. The current transducer according to any one of the preceding claims, further comprising a primary conductor (5), and the primary conductor includes a first connection terminal (110a) and a second connection terminal (110b).

4. The current transducer according to the preceding claim, wherein the primary conductor includes an intermediate portion interconnecting the first connection terminal and the second connection terminal, and the intermediate portion has a first branch (106a), a second branch (106b), and a bridging branch (108) interconnecting one end of the first branch and one end of the second branch, and the first branch and the second branch are separated by a gap (G).

5. The current transducer according to claim 3, wherein the primary conductor includes an intermediate portion interconnecting the first connection terminal and the second connection terminal, and the intermediate portion has a reduced cross-sectional area compared to the first connection terminal and the second connection terminal, and the first connection terminal and the second connection terminal are separated by a gap (G).

6. The current transducer according to any one of claims 3-5, wherein the magnetic field gradient sensor (2) is mounted on the surface of the primary conductor, and the surface of the primary conductor is separated from the magnetic field gradient sensor by an insulating layer.

7. The current transducer according to any one of the preceding claims 3-6, wherein in addition to the connection terminals of the primary conductor and the secondary conductor arrangement, the primary conductor (105), the secondary conductor arrangement (114), and the magnetic field gradient sensor (2) are overmolded by an insulating housing (104).

8. The current transducer according to any one of the preceding claims 3-7, wherein the primary conductor and the secondary conductor arrangement are formed by a lead frame.

9. The current transducer according to any one of the preceding claims, wherein each TMR resistor includes a plurality of TMR elements, and the plurality of TMR elements are connected in series through conductive interconnect track portions (18).

10. The current transducer according to the preceding claim, wherein the number of the plurality of TMR elements of each TMR half-resistor is greater than one hundred.

11. The current transducer according to the preceding claim, wherein the interconnect track portions are arranged on at least a first layer and a second layer of the substrate, and the TMR elements form an interconnection between the first layer and the second layer.

12. The current transducer according to the preceding claim, wherein each TMR resistor portion includes a pinned ferromagnetic layer mounted on the first layer of the substrate and a free ferromagnetic layer mounted on the second layer of the substrate.

13. The current transducer according to any one of the preceding claims 9 - 12, wherein the TMR elements of the plurality of TMR elements are spaced apart from adjacent serially connected TMR elements at substantially equal distances.

14. The current transducer according to any one of the preceding claims 9 - 13, wherein the TMR elements of each TMR half - resistor are arranged at positions extending from a central region of the die substrate to a position close to the outer boundary of the die substrate.

15. The current transducer according to any one of the preceding claims, wherein the respective TMR sensor terminals (14) comprise a pair of said output terminals (14a, 14b) and a pair of said supply terminals (14c, 14d), with each terminal arranged at the outer corners (8) of four quadrants.

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