Stray magnetic field resistant magnetoresistive bridge circuit

Abstract

A magnetic field sensor is described having at least two bridges including MR elements. The MR elements of each bridge have a different magnetic reference direction. The first bridge is arranged to detect a first uniform magnetic field of a first polarity, and the second bridge is arranged to detect a second uniform magnetic field of a second polarity opposite to the first polarity. The first and second uniform magnetic fields constitute a differential magnetic field of interest. The described magnetic field sensor detects the magnetic field of interest in a manner that is immune to stray magnetic fields. Dual signal path embodiments are described in which the outputs of the two bridges are processed independently, and single signal path embodiments include a single signal path for processing the output of a combined (e.g., parallel) bridge arrangement.

Description

[Technical Field]

[0001]

[0001] The present disclosure relates generally to magnetic field sensors, and more particularly to magnetic field sensors including magnetoresistive bridge circuits that are resistant to stray magnetic fields. [Background technology]

[0002]

[0002] Magnetic field sensors utilize various types of magnetic field sensing elements, e.g., Hall effect elements and magnetoresistive elements, which are often coupled to electronic circuits on a common substrate. Some magnetic field sensors include magnetoresistive (MR) elements, such as giant magnetoresistive (GMR) elements and tunneling magnetoresistive (TMR) elements. Generally, GMR and TMR elements have relatively high sensitivity compared to, for example, Hall effect elements.

[0003]

[0003] Magnetic field sensors are used in a variety of applications, including, but not limited to, angle sensors that detect the angle of a magnetic field direction, current sensors that detect a magnetic field generated by the flow of current through a conductor, magnetic switches that detect the proximity of a ferromagnetic object, motion detectors that detect rotational and / or linear motion, for example, the movement of a ferromagnetic article in the form of a ring magnet or magnetic region of a ferromagnetic target (e.g., a gear tooth) passing by, where the magnetic field sensor is used in combination with a back-biased magnet or other magnet, and magnetic field sensors that detect the magnetic field density of a magnetic field.

[0004]

[0004] Various parameters characterize the performance of magnetic field sensors and magnetic field sensing elements. With respect to magnetic field sensing elements, the parameters include sensitivity, which is the change in the output signal of the magnetic field sensing element in response to a change in the magnetic field, and linearity, which is the degree to which the output signal of the magnetic field sensing element changes linearly (i.e., in direct proportion) to the magnetic field.

[0005] The accuracy with which a magnetic field sensor detects a magnetic field of interest can be adversely affected by the presence of stray magnetic fields (ie, magnetic fields other than the magnetic field of interest to be detected). Summary of the Invention

[0006] The present disclosure provides a magnetic field sensor having two or more bridge configurations of MR elements. The MR elements of the first and second bridges have different magnetic reference directions. The first bridge is arranged to detect a first uniform magnetic field of a first polarity, and the second bridge is arranged to detect a second uniform magnetic field of a second polarity opposite the first polarity. The first and second uniform magnetic fields constitute a differential magnetic field of interest. The described magnetic field sensor is configured to detect the magnetic field of interest in a manner that is immune to stray magnetic fields. Dual signal path embodiments are described in which the outputs of the two bridges are processed independently, and single signal path embodiments are described in which a single output of the combined (e.g., parallel) bridge arrangement is processed.

[0007] According to the present disclosure, a magnetic field sensor includes a first bridge and a second bridge. The first bridge includes a first MR element, a second MR element, a third MR element, and a fourth MR element, where the first MR element is coupled between a power supply and a first output node, the second MR element is coupled between a power supply and a second output node, the third MR element is coupled between the second output node and ground, and the fourth MR element is coupled between the first output node and ground. The second bridge includes a fifth MR element, a sixth MR element, a seventh MR element, and an eighth MR element, where the fifth MR element is coupled between the power supply and a third output node, the sixth MR element is coupled between the power supply and a fourth output node, the seventh MR element is coupled between the fourth output node and ground, and the eighth MR element is coupled between the third output node and ground. The first MR element, the third MR element, the fifth MR element, and the seventh MR element each have a first magnetic reference direction, and the second MR element, the fourth MR element, the sixth MR element, and the eighth MR element each have a second magnetic reference direction opposite to the first magnetic reference direction.

[0008] Features may include one or more of the following features individually or in combination with other features: the first bridge may be arranged to detect a first uniform magnetic field of a first polarity, and the second bridge may be arranged to detect a second uniform magnetic field of a second polarity opposite to the first polarity, the first uniform magnetic field and the second uniform magnetic field being generated by a common magnetic field source and having equal magnitude.

[0009] In some embodiments, the first electrical signal between the first output node and the second output node represents a first uniform magnetic field, and the second electrical signal between the third output node and the fourth output node represents a second uniform magnetic field. The magnetic field sensor can further include a subtraction element coupled to receive the first electrical signal and the second electrical signal and configured to generate a subtraction signal representing a difference between the first electrical signal and the second electrical signal, the subtraction signal being independent of stray magnetic fields and representing the magnitude of the first uniform magnetic field.

[0010] In some embodiments, the first output node and the third output node are electrically coupled together, and the second output node and the fourth output node are electrically coupled together. The power source may be a current source, and a differential current signal between the first output node and the second output node is independent of stray magnetic fields and represents the magnitude of the first uniform magnetic field.

[0011] The first and second uniform magnetic fields may be generated by a current conductor. The first and second uniform magnetic fields may be generated by the movement of a ferromagnetic object. Each of the first, second, third, fourth, fifth, sixth, seventh, and eighth MR elements may be a TMR element. The first, third, fifth, and seventh MR elements may be repinned to have a first magnetic reference direction, or the second, fourth, sixth, and eighth MR elements may be repinned to have a second magnetic reference direction.

[0012]

[0012] Further described is a magnetic field sensor including a first bridge having a first MR element, a second MR element, a third MR element, and a fourth MR element, wherein the first MR element is coupled between a power supply and a first output node, the second MR element is coupled between a power supply and a second output node, the third MR element is coupled between the second output node and ground, and the fourth MR element is coupled between the first output node and ground; the magnetic field sensor further includes a second bridge having a fifth MR element, a sixth MR element, a seventh MR element, and an eighth MR element, wherein the fifth MR element is coupled between the power supply and the third output node, the sixth MR element is coupled between the power supply and the fourth output node, the seventh MR element is coupled between the fourth output node and ground, and the eighth MR element is coupled between the third output node and ground. The first bridge is positioned to detect a first uniform magnetic field of a first polarity, and the second bridge is positioned to detect a second uniform magnetic field of a second polarity opposite to the first polarity, the first uniform magnetic field and the second uniform magnetic field being generated by a common magnetic field source and having equal magnitude.

[0013]

[0013] Features may include one or more of the following features individually or in combination with other features: the first MR element, the third MR element, the fifth MR element, and the seventh MR element each have a first magnetic reference direction, and the second MR element, the fourth MR element, the sixth MR element, and the eighth MR element each have a second magnetic reference direction opposite to the first magnetic reference direction.

[0014] In some embodiments, the first electrical signal between the first output node and the second output node represents a first uniform magnetic field, and the second electrical signal between the third output node and the fourth output node represents a second uniform magnetic field. The magnetic field sensor can further include a subtraction element coupled to receive the first electrical signal and the second electrical signal and configured to generate a subtraction signal representing a difference between the first electrical signal and the second electrical signal, the subtraction signal being independent of stray magnetic fields and representing the magnitude of the first uniform magnetic field.

[0015] In some embodiments, the first output node and the third output node are electrically coupled together, and the second output node and the fourth output node are electrically coupled together. The power source may be a current source, and a differential current signal between the first output node and the second output node is independent of stray magnetic fields and represents the magnitude of the first uniform magnetic field.

[0016] The first and second uniform magnetic fields may be generated by a current conductor. The first and second uniform magnetic fields may be generated by the movement of a ferromagnetic object. Each of the first, second, third, fourth, fifth, sixth, seventh, and eighth MR elements may be a TMR element. The first, third, fifth, and seventh MR elements may be repinned to have a first magnetic reference direction, or the second, fourth, sixth, and eighth MR elements may be repinned to have a second magnetic reference direction.

[0017]

[0017] The foregoing features can be more fully understood from the following description of the drawings. The drawings aid in explaining and understanding the disclosed technology. Because it is often impractical or impossible to illustrate and describe every possible embodiment, the drawings provided depict one or more exemplary embodiments. Thus, the drawings are not intended to limit the scope of the broad concepts, systems, and techniques described herein. Like numbers in the drawings represent like elements. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram of an exemplary magnetometer bridge including tunneling magnetoresistive (TMR) elements. [Figure 2]

[0019] FIG. 1 shows a circuit including two magnetometer bridges, each having a TMR element. [Figure 3]

[0020] FIG. 3 is a diagram showing a current sensor configuration including the circuit of FIG. 2. [Figure 3A]

[0021] FIG. 3 is a diagram showing a rotation sensor configuration including the circuit of FIG. 2. [Figure 4]

[0022] FIG. 1 shows a circuit including a compound magnetometer bridge, with the elements of each bridge connected in series. [Figure 5]

[0023] FIG. 5 is a diagram showing a current sensor configuration including the circuit of FIG. 4. [Figure 5A]

[0024] FIG. 5 is a diagram showing a rotation sensor configuration including the circuit of FIG. 4. [Figure 6]

[0025] FIG. 10 shows another circuit including two magnetometer bridges, each with a TMR element, with the two bridges connected in parallel. [Figure 7]

[0026] FIG. 7 is a diagram showing a current sensor configuration including the circuit of FIG. 6. [Figure 7A]

[0027] FIG. 7 is a diagram showing a rotation sensor configuration including the circuit of FIG. 6. [Figure 8]

[0028] 7 is a schematic diagram of a current sensor of a type including the bridge of FIG. 2 or the bridge of FIG. 6; [Figure 9]

[0029] 7 is a schematic diagram of a motion / rotation sensor of the type including the bridge of FIG. 2 or the bridge of FIG. 6. DETAILED DESCRIPTION OF THE INVENTION

[0019]

[0030] 1, magnetometer bridge circuit 100 includes four magnetoresistive (MR) elements R1, R2, R3, and R4 arranged in a bridge configuration. The first MR element R1 is coupled between a positive power supply connection 104 and a first output node 110. The second MR element R2 is coupled between the positive power supply connection 104 and a second output node 114. The third MR element R3 is coupled between the second output node 114 and a negative power supply connection 106. The fourth MR element R4 is coupled between the first output node 110 and the negative power supply connection 106. Each MR element R1-R4 can be considered to establish a respective leg of bridge 100.

[0020]

[0031] The power supplies connected to the positive connection 104 and the negative connection 106 can take the form of a voltage source or a current source. In embodiments utilizing a voltage source, the positive power supply connection 104 can be connected to the Vsup terminal as shown, and the negative power supply connection 106 can be connected to ground GND as shown. In such a configuration, the resistance of the MR elements R1-R4 changes in response to a magnetic field. In embodiments utilizing a current source (e.g., FIG. 6), the positive power supply connection 104 can be connected to the source terminal of the current source, and the negative power supply connection 106 can be connected to the return terminal of the current source. In such a current-driven configuration, the conductance of the MR elements changes in response to a magnetic field. Thus, although the power supply shown in FIG. 1 is a voltage source, the power supply may alternatively be a current source.

[0021]

[0032] The first output node 110 and the second output node 114 of the bridge 100 are labeled OUTp and OUTn, respectively. Those skilled in the art will appreciate that the output nodes 110, 114 can be voltage output nodes or current output nodes. In other words, the voltage output signals obtained from the first and second output nodes 110, 114 can be proportional to the detected magnetic field, or the current output signals obtained from the first and second output nodes 110, 114 can be proportional to the detected magnetic field. The monitored parameter may be selected based on its linearity with respect to the magnetic field. In the illustrated configuration, conductance tends to be more linear than resistance with respect to the TMR element.

[0022]

[0033] It will thus be appreciated that there are four possible combinations of supplying bridge 100 and sensing its output. When the sensed and supplied variables are different (i.e., voltage drive and current sense, or current drive and voltage sense), the output is not normalized. In some cases, normalization (i.e., driving and sensing the bridge with the same parameter, voltage or current) may be desirable to avoid the adverse effects of process and manufacturing variations.

[0023]

[0034] As known to those skilled in the art, an MR element, such as elements R1-R4, may include a substrate on which a reference layer is formed. A free layer may be formed on the reference layer, separated from the reference layer by a spacer. Both the reference layer and the free layer are magnetic layers, and the layered arrangement of the MR element may be referred to as an MR stack.

[0024]

[0035] The magnetization orientation of the reference layer is fixed and intended to be co-linear with the magnetic field to be sensed, while the magnetization orientation of the free layer is free to align with the magnetic field of the surrounding environment. The resistance of the MR element is proportional to the angle of magnetization of the free layer relative to the angle of magnetization of the reference layer.

[0025]

[0036] As shown and described in U.S. Pat. No. 11,346,894, entitled "Current Sensor for Compensation of On-die Temperature Gradient," issued May 31, 2022, and incorporated herein by reference, the resistance of the MR element is at its maximum when the free and reference layers have the same magnetization orientation, while the resistance of the MR element is at its minimum when the reference and free layers have opposite magnetization orientations. The present disclosure is not limited to any particular implementation of the MR element.

[0026]

[0037] The term "pinning direction" or "magnetic reference direction" of an MR element refers to the orientation of magnetization in a reference layer (or layers) of the MR element. The pinning direction of an MR element determines whether the resistance of the MR element increases or decreases when the MR element is subjected to a magnetic field having a particular orientation or angle relative to the pinning of such reference layer. In particular, when considering a magnetic field that is colinear with the pinning direction of the reference layer, the resistance of the element increases with increasing detected magnetic field strength when the magnetic field is opposite the magnetic reference direction, but decreases with increasing magnetic field strength when the magnetic field is aligned with the magnetic reference direction.

[0027]

[0038] The sensitivity of the MR bridge 100 is based on the sensitivity of the MR stacks of elements R1-R4 to stray magnetic fields, and further based on the sensitivity of the bridge configuration itself to stray magnetic fields. The sensitivity of the MR stacks of elements R1-R4 to stray magnetic fields depends on the stack characteristics and how robust their parametric behavior can be in the presence of stray magnetic fields. For the purposes of this disclosure, it is assumed that the MR stacks of elements R1-R4 are not affected by stray magnetic fields. Therefore, this disclosure focuses on the sensitivity of the described bridge configuration itself to stray magnetic fields, which sensitivity depends on the way a particular bridge is arranged and the quality (i.e., mismatch) of the manufacturing process.

[0028]

[0039] MR stacks suitable for use in fabricating elements R1-R4, and other bridge-configured elements herein, are described in U.S. Pat. No. 11,346,894, issued May 31, 2022, entitled "Current Sensor for Compensation of On-die Temperature Gradient," which is incorporated herein by reference, and further described in U.S. Pat. No. 11,127,518, issued September 21, 2021, entitled "Tunnel Magnetoresistance (TMR) Element having Cobalt Iron and Tantalum Layers," which is incorporated herein by reference.

[0029]

[0040] Each of the MR elements R1-R4 has a respective magnetic reference or pinning direction, indicated by a solid arrow. Thus, MR elements R1 and R3 have a first pinning direction 120, and MR elements R2 and R4 have a second pinning direction 122 that is opposite to the first pinning direction. In this and other paragraphs herein, "opposite" pinning directions means that the pinning directions are 180 degrees apart. However, those skilled in the art will appreciate that alternative implementations are possible in which the opposite pinning directions 120, 122 may differ by less than or more than 180 degrees. However, for linear differential detection, the pinning directions 120, 122 should be 180 degrees apart because otherwise they would not be colinear with the applied magnetic field, resulting in a mismatch in sensitivity levels due to the TMR elements not being 180 degrees opposite. In other words, in general, for linear detection using TMR elements, it is advantageous for the applied magnetic field to be collinear with the pinning direction to maximize sensitivity.

[0030]

[0041] Establishing the illustrated magnetic reference directions 120, 122 may require repinning of two of the four MR elements R1-R4. This is because the MR elements R1-R4 are fabricated on a single substrate using the same materials and process parameters, and therefore the resulting MR elements will initially have the same pinned direction. Repinning is a process in which the magnetic reference direction of an MR element is changed. Repinning is accomplished at a specific temperature and applied magnetic field level and involves "printing" a new magnetic reference onto the MR element. Typically, a high magnetic field strength, such as greater than 5000 gauss, is required. Heating softens the material to facilitate modification and may require temperatures in excess of 250°C, such as can be achieved with a laser or current flow. When "magnetic field printing or pinning" is performed, the application of heat should be localized to the MR element being repinned so that it affects only the element being heated, not other elements that will also be exposed to the high magnetic field strength. Laser pinning achieves localized, spatially precise heating by focusing a laser beam onto the TMR element to be repinned, whereas pinning by applying a current requires forcing a current through the TMR element being repinned in order to heat it, and therefore requires dedicated circuitry for this purpose.

[0031]

[0042] Based on the bridge configuration of MR elements R1-R4 and the magnetic reference direction, bridge 100 generates an output signal (e.g., output voltage V=OUTp-OUTn) that varies with variations in the strength of the magnetic field uniformly experienced by each of elements R1-R4. In other words, magnetometer bridge 100 detects a uniform magnetic field across all of bridge elements R1-R4 and cancels any differential magnetic field effects on the elements. This is because a differential magnetic field should change the resistance of elements R3 and R4 by the same amount and in the same direction (i.e., increase or decrease resistance), and therefore there should be no change in the bridge output signal as a result of the differential magnetic field. "Uniform" means that the detected magnetic field has the same magnitude and direction for all of bridge elements R1-R4.

[0032]

[0043] In the context of FIG. 1 , bridge 100 is configured to detect a uniform magnetic field 130 having a direction indicated by the cross-hatched arrow labeled 130. Magnetic field 130 may be referred to as the magnetic field of interest, the applied magnetic field, or the detected magnetic field that bridge 100 is configured to detect. Alternatively or additionally, magnetic field 130 may be a stray magnetic field from a source other than the source of the magnetic field of interest. Thus, because bridge 100 is configured to detect magnetic field 130 that is uniform across all of MR elements R1-R4, bridge 100 is susceptible to stray magnetic fields that, by their nature, affect all of the bridge elements in the same direction. In other words, bridge 100 cannot distinguish between the magnetic field of interest and the stray magnetic field.

[0033]

[0044] Advantageously, however, the sensitivity of bridge 100 is not modulated by stray magnetic fields, as can be seen below.

[0034]

number

[0035] In this equation, RA is the resistance of elements R1 and R3, RB is the resistance of elements R2 and R4, and S T is the element sensitivity in Ω / G, and ΔS T is the sensitivity mismatch with respect to other elements in the bridge, and R O is the rated resistance of the MR element when no magnetic field is applied, and ΔR off is the electrical mismatch between the elements in the bridge, Bs is the stray magnetic field, and Bin is the magnetic field of interest to be detected. In particular, the sensitivity S for element RA T is of opposite polarity to that for element RB due to repinning.

[0036]

[0045] Bridge output voltage V O_TMR_M_VD =OUTp-OUTn can be given by:

[0037]

number

[0038]

[0046] In implementations where the magnetometer bridge 100 is driven by current (e.g., FIG. 6), the bridge output voltage V O_TMR_M_CD =OUTp-OUTn can be expressed as follows:

[0039]

number

[0040]

[0047] Equations (2) and (3) can be simplified to equations (4) and (5), respectively, by assuming no mismatch and an ideal linear stack. From equations (4) and (5), it can be noticed that the sensitivity of the bridge is not modulated by the stray field Bs. Rather, the stray field Bs represents an additional term:

[0041]

number

[0042]

[0048] From the above discussion, it will be appreciated that the magnetometer bridge 100, while unable to distinguish stray magnetic fields from magnetic fields of interest, has the advantageous attribute of sensitivity that is not modulated by the effects of stray magnetic fields. To address the additional effects of stray magnetic fields Bs in accordance with the present disclosure, two magnetometer bridges of the type shown and described in conjunction with FIG. 1 may be used in a configuration in which the stray magnetic field is presented to the bridges in a differential fashion.

[0043]

[0049] 2, in accordance with an embodiment of the present disclosure, a magnetometer bridge circuit 200 includes two bridge circuits or bridges 204, each type of which is shown and described in conjunction with FIG. 1, but with one such bridge positioned to detect positive magnetic fields and the other bridge positioned to detect negative magnetic fields. An example application of circuit 200 is shown and described in conjunction with FIGS. 3 and 3A.

[0044]

[0050] The first bridge 204 includes a first MR element R1, a second MR element R2, a third MR element R3, and a fourth MR element R4. The first MR element R1 is coupled between a power supply Vsup and a first output node 210. The second MR element R2 is coupled between a power supply Vsup and a second output node 214. The third MR element R3 is coupled between the second output node 214 and ground. The fourth MR element R4 is coupled between the first output node 210 and ground.

[0045]

[0051] The second bridge 208 includes a fifth MR element R5, a sixth MR element R6, a seventh MR element R7, and an eighth MR element R8. The fifth MR element R5 is coupled between the power supply and the third output node 216, the sixth MR element R6 is coupled between the power supply and the fourth output node 218, the seventh MR element R7 is coupled between the fourth output node 218 and ground, and the eighth MR element R8 is coupled between the third output node 216 and ground.

[0046]

[0052] The first MR element R1, the third MR element R3, the fifth MR element R5, and the seventh MR element R7 each have a first magnetic reference direction labeled 220. The second MR element R2, the fourth MR element R4, the sixth MR element R6, and the eighth MR element R8 each have a second magnetic reference direction labeled 222 that is opposite (i.e., 180 degrees different from) the first magnetic reference direction 220.

[0047]

[0053] In this example, each of the MR elements R1-R8 is a tunneling magnetoresistive (TMR) element, although alternative implementations are possible in which at least some (or all) of the MR elements R1-R8 may be giant magnetoresistive (GMR) elements or other suitable types of MR elements, such as anisotropic magnetoresistive (AMR) elements or magnetic tunnel junctions (MTJ).

[0048]

[0054] To use the two-bridge circuit 200 to detect a magnetic field of interest in a manner immune to stray magnetic fields, the bridges 204, 208 are arranged to detect a differential magnetic field, such that the first bridge 204 is arranged to detect a first uniform magnetic field of a first polarity indicated by arrow 230, and the second bridge 208 is arranged to detect a second uniform magnetic field of a second polarity opposite to the first polarity indicated by arrow 240, the first uniform magnetic field and the second uniform magnetic field being generated by a common magnetic field source and having equal magnitude.

[0049]

[0055] 3 and 3A show exemplary sources of differential magnetic fields including uniform magnetic fields of opposite polarity, such as magnetic fields 230 and 240. Suffice it to say that a first electrical signal V1 between first output node 210 and second output node 214 represents first uniform magnetic field 230, and a second electrical signal V2 between third output node 216 and fourth output node 218 represents second uniform magnetic field 240.

[0050]

[0056] In use, the output signals V1, V2 of bridges 204, 208, respectively, are processed by circuitry configured to subtract one such output signal from the other. Exemplary circuitry is shown and described in conjunction with exemplary schematic diagrams in Figures 8 and 9. The processing circuitry may include a subtraction element coupled to receive the first electrical signal V1 and the second electrical signal V2 and configured to generate a subtraction signal V1-V2 representing the difference between the first and second electrical signals. The resulting subtraction signal represents the magnitude of the first uniform magnetic field and is not affected by stray magnetic fields.

[0051]

[0057] More specifically, the output voltage V1 of the bridge 204 can be expressed as:

[0052]

number

[0053] Then, the output voltage V2 of the bridge 208 can be expressed as:

[0054]

number

[0055]

[0058] The result of subtracting the voltage in equation (7) from the voltage in equation (6) can be expressed as:

[0056]

number

[0057] In particular, considering the same imbalance for both bridges, i.e.,

number

[0058]

number

[0059]

[0059] By examining equation (8), it can be seen that the stray field immunity (with respect to stray fields collinear with the pinning reference) is proportional to the element sensitivity mismatch ΔS in one bridge 204. T1 and the corresponding mismatch ΔS in the element sensitivity in the other bridge 208. T2 the difference between (i.e., ΔS T1 -ΔS T2 ) when the mismatch is the same on both bridges (although different from zero), the modulation of the output voltage as a function of the stray magnetic field is very weak (considering the squared term in the denominator). Thus, the two-bridge circuit 200 of FIG. 2 has the advantage of being more robust against stray magnetic fields (e.g., compared to a single-bridge solution such as bridge 100 of FIG. 1). Furthermore, the mismatch in the electrical offsets also contributes to the imbalance (i.e., ΔR) between bridge 204 and bridge 208. off1 -ΔR off2) differ. In other words, use of the two-bridge circuit 200 does not require zero mismatch (sensitivity or electrical offset) to achieve stray field rejection; rather, it is desirable to have similar mismatch within each of the bridges 204, 208. In other words, in a single bridge (e.g., bridge 100 of FIG. 1), the mismatch between elements R1-R4 within the bridge affects the bridge output voltage, but in the case of a two-bridge (e.g., circuit 200 of FIG. 2), it is only the difference in relative mismatch between the two bridges 204, 208 that primarily affects the output voltage.

[0060] Continuing with reference to FIG. 3, current sensor 300 includes a current conductor 350 and bridge circuits 304, 308. Current conductor 350 is configured to pass a current indicated by arrow 352. Current 352 generates a magnetic field that is detected by bridges 304, 308, which may be the same as or similar to bridges 204, 208 of FIG. 2. To this end, bridge 304 includes a first MR element R1, a second MR element R2, a third MR element R3, and a fourth MR element R4. First MR element R1 is coupled between a power supply Vsup and a first output node 310. Second MR element R2 is coupled between a power supply Vsup and a second output node 314. Third MR element R3 is coupled between second output node 314 and ground. Fourth MR element R4 is coupled between first output node 310 and ground. The second bridge 308 includes a fifth MR element R5, a sixth MR element R6, a seventh MR element R7, and an eighth MR element R8. The fifth MR element R5 is coupled between the power supply and a third output node 316, the sixth MR element R6 is coupled between the power supply and a fourth output node 318, the seventh MR element R7 is coupled between the fourth output node 318 and ground, and the eighth MR element R8 is coupled between the third output node 316 and ground.

[0061] Each of the first MR element R1, the third MR element R3, the fifth MR element R5, and the seventh MR element R7 has a first magnetic reference direction labeled 320. Each of the second MR element R2, the fourth MR element R4, the sixth MR element R6, and the eighth MR element R8 has a second magnetic reference direction labeled 322 that is opposite (i.e., 180 degrees different from) the first magnetic reference direction 320. In this example, each of the MR elements R1-R8 is a TMR element, although alternative sensing element types are acceptable.

[0062] Bridges 304, 308 are arranged to differentially detect a magnetic field of interest generated by current 352. In particular, bridge 304 is arranged to detect a uniform magnetic field indicated by arrow 330 (which may be the same as or similar to magnetic field 230), and bridge 308 is arranged to detect a uniform magnetic field indicated by arrow 340 (which may be the same as or similar to magnetic field 240), the uniform magnetic fields 330, 340 having opposite polarities and equal magnitudes. The magnitudes of magnetic fields 330, 340 are equal because such fields are generated by a common source, i.e., current 352 passing through a conductor.

[0063] The opposing polarities of the magnetic fields 330, 340 are achieved by the design of the conductor 350 and the placement of the bridges 304, 308 relative to the conductor.

[0064]

[0063] The orientation of bridge elements R1 to R8 relative to conductor 350 is such that the magnetic field generated by current 352 has a component parallel to the axis of maximum sensitivity, and that axis of maximum sensitivity for MR elements R1 to R8 is parallel to the substrate or within the plane of the substrate supporting the magnetic field detection elements.

[0065] Various physical configurations are possible for implementing the current sensor 300. For example, the current sensor 300, including the bridges 304, 308, may be provided in the form of an integrated circuit (IC) with the conductors 350 integrated into the integrated circuit package (i.e., the conductors may be formed within the same IC package, for example, in the form of bus bars or current traces). However, alternatively, the conductors 350 may be external to the current sensor IC package that includes the bridges 304, 308 and, optionally, further processing circuitry.

[0066]

[0065] Bridges 304, 308 may be fabricated on a single or multiple substrates, such as a semiconductor die, to support MR elements R1-R8 and, optionally, further processing circuitry. For example, bridges 304, 308 may be fabricated on a single substrate (e.g., a semiconductor die) within a single IC package, or alternatively, may be fabricated on separate substrates within one or more IC packages.

[0067]

[0066] The bridges 304, 308 may be arranged relative to the conductor 350 in different ways depending on the particular application, so long as the uniform magnetic fields 330, 340 that constitute the magnetic field to be detected are sensed by the MR detection elements R1-R8 having directional components aligned with the axis of maximum sensitivity (i.e., so that the MR elements R1-R8 detect in-plane differential components).

[0068] 3A, rotational sensor system 360 includes target 364 and sensor 370. Sensor 370 includes bridges 304, 308, which are the bridges described above. Target 364 can take a variety of forms, such as the illustrated rotating gear having features including teeth 366a and valleys 366b, or a ring-shaped magnet with magnetic regions of alternating polarity. For example, gear 364 may be ferromagnetic and positioned adjacent to a permanent magnet (not shown) such that a fluctuation occurs in the magnetic field upon movement of the gear in a so-called "back bias" configuration.

[0069]

[0068] The movement (e.g., rotation) of the target 364 generates a magnetic field including a first uniform magnetic field 330 to which one of the bridges 304 is exposed and a second uniform magnetic field 340 to which another of the bridges 308 is exposed. The first and second uniform magnetic fields 330, 340 have opposite polarities as indicated by the arrows 330, 340, which have directions that are 180 degrees apart.

[0070]

[0069] Thus, bridges 304, 308 are positioned to differentially detect magnetic fields of interest indicative of the movement of target 364 based on the movement of target 364. In particular, bridge 304 is positioned to detect a uniform magnetic field indicated by arrow 330 (which may be the same as or similar to magnetic field 230), and bridge 308 is positioned to detect a uniform magnetic field indicated by arrow 340 (which may be the same as or similar to magnetic field 240), the uniform magnetic fields 330, 340 having opposite polarities and equal magnitudes. In rotation sensor 360 of Figure 3A, the opposite polarities of magnetic fields 330, 340 are achieved by the movement of target 364 past the sensor, such that bridge 304 is positioned to sense magnetic field direction 330, and bridge 308 is positioned to sense magnetic field direction 340. In particular, the sensor die may be aligned with a rotating target, and the bridges 304, 308 may be spaced apart from one another by a distance based on the size and spacing of the target features 366a, 366b (i.e., the size of the tooth-valley pairs relative to the spacing between the bridges). The orientation of the bridge elements R1-R8 relative to the target 364 is such that the magnetic field associated with target motion has a component parallel to the axis of maximum sensitivity, and that axis of maximum sensitivity for the MR elements R1-R8 is parallel to the substrate or in the plane of the substrate supporting the magnetic field sensing elements. The magnitudes of the magnetic fields 330, 340 are equal because such fields are generated by a common source, i.e., by the motion of the target 364.

[0071] Various physical configurations are possible for implementing rotation sensor system 360. Sensor 370, including bridges 304, 308, may be provided in the form of an integrated circuit including single or multiple substrates, such as semiconductor dies, for supporting MR elements R1-R8 and, optionally, further processing circuitry. For example, bridges 304, 308 may be fabricated on a single substrate (e.g., a semiconductor die) within a single IC package, or alternatively, may be fabricated on separate substrates within one or more IC packages.

[0072] The sensor IC 370 may be positioned relative to the target 364 in different ways depending on the particular application, so long as the uniform magnetic fields 330, 340 that constitute the magnetic field to be detected are felt by the MR sensing elements R1-R8 with directional components aligned with the plane of sensitivity. For example, although shown in a plan view, the sensor IC 370 may be rotated by 90 degrees so that the detected magnetic fields 330, 340 are coplanar with the major surface of the semiconductor die. Furthermore, such a sensor IC 370 may be rotated by 90 degrees out of the plane of the page so that one bridge 304 is closer to the target 364 than the other bridge 308. In general, the detected magnetic fields 330, 340 should oppose each other and be in-plane with respect to the sensor die.

[0073] 4, an alternative bridge circuit 400 can include a compound bridge arrangement including eight MR elements R1-R8. Bridge 400 includes, as shown, a first MR element R1 and a sixth MR element R6 coupled in series to form a first bridge leg between a power supply Vsup and a first output node 410, a second MR element R2 and a seventh MR element R7 coupled in series to form a second bridge leg between the power supply Vsup and a second output node 414, a third MR element R3 and an eighth MR element R8 coupled in series to form a third bridge leg between the second output node 414 and ground, and a fourth MR element R4 and a fifth MR element R5 coupled in series to form a fourth bridge leg between the first output node 410 and ground.

[0074] Each of the first MR element R1, the third MR element R3, the fifth MR element R5, and the seventh MR element R7 has a first magnetic reference direction labeled 420. Each of the second MR element R2, the fourth MR element R4, the sixth MR element R6, and the eighth MR element R8 has a second magnetic reference direction labeled 422 that is opposite (i.e., 180 degrees different from) the first magnetic reference direction 420. Thus, in each leg of the bridge 400, the MR elements have different pinning directions that are opposite to each other. In this example, each of the MR elements R1-R8 is a TMR element, although alternative sensing element types are acceptable.

[0075]

[0074] Bridge 400 is configured to detect a differential magnetic field of interest consisting of a first uniform magnetic field represented by arrows labeled 430 and a second uniform magnetic field represented by arrows labeled 440 in a stray magnetic field-rejecting manner when the stray magnetic field can affect bridge elements R1-R8. More specifically, bridge elements R1-R4 are arranged to detect the first uniform magnetic field of a first polarity 430, and bridge elements R5-R8 are arranged to detect the second uniform magnetic field of a second polarity 440 opposite to the first polarity, the first uniform magnetic field and the second uniform magnetic field being generated by a common magnetic field source and having equal magnitude.

[0076] Bridge circuit 400 can be represented as a series-coupled bridge configuration, or a compound bridge configuration, and unlike bridge circuit 200 of Figure 2, which requires two signal processing paths, it requires only a single signal processing path, thereby saving power and area because the single output signal across nodes 410, 414 has the subtraction operation already implemented by the electrical connections of the elements in the bridge (e.g., the subtraction of output signal V2 from V1 in Figure 2).

[0077]

[0076] With further reference to Figures 5 and 5A, possible application circuits for use with the composite series-coupled bridge circuit 400 of Figure 4 include a current sensor 500 and a rotation sensor 560, respectively.

[0078]

[0077] Figure 5 shows a current sensor 500, which may be the same as or similar to current sensor 300 of Figure 3, and therefore includes a current conductor 550 configured to carry a current indicated by arrow 552. Current 552 generates a magnetic field that is detected by bridge 400 of Figure 4, which includes MR elements R1-R8 arranged and having magnetic reference directions as shown.

[0079]

[0078] MR elements R1-R8 are arranged to differentially detect the magnetic field of interest generated by current 552. In particular, bridge elements R1-R4 are arranged to detect a uniform magnetic field indicated by arrow 430 (which may be the same as or similar to magnetic field 230 or 330), and bridge elements R5-R8 are arranged to detect a uniform magnetic field indicated by arrow 440 (which may be the same as or similar to magnetic field 240 or 340), the uniform magnetic fields 430, 440 having opposite polarities and equal magnitudes.

[0080]

[0079] The electrical connections of the MR elements R1 to R8 are as shown in Figure 4, and the physical configuration of the MR elements can be designed to suit the particular application described above in conjunction with the current sensor 300 of Figure 3.

[0081]

[0080] Figure 5A shows rotation sensor 560, which may be the same as or similar to rotation sensor 360 of Figure 3A, and thus includes target 364. Rotation of target 364 generates a magnetic field that is detected by bridge 400 of Figure 4, which includes MR elements R1-R8 arranged as shown and having magnetic reference directions.

[0082]

[0081] MR elements R1-R8 are arranged to differentially detect the rotating, subject magnetic field generated by target 364. In particular, bridge elements R1-R4 are arranged to detect a uniform magnetic field indicated by arrow 430 (which may be the same as or similar to magnetic field 230 or 330), and bridge elements R5-R8 are arranged to detect a uniform magnetic field indicated by arrow 440 (which may be the same as or similar to magnetic field 240 or 340), the uniform magnetic fields 430, 440 having opposite polarities and equal magnitudes.

[0083]

[0082] The electrical connections of the MR elements R1 to R8 are as shown in Figure 4, and the physical configuration of the MR elements can be designed to suit the particular application described above in conjunction with the rotation sensor 360 of Figure 3A.

[0084]

[0083] With further reference to Figure 6, as shown, an alternative bridge circuit 600 includes two bridges where the supply and output connections of the two bridges are electrically coupled together, resulting in the bridges being coupled in parallel. In the embodiment of Figure 6, bridge circuit 600 is supplied by a current source Icc, and therefore it is the conductance of the MR elements that changes with changing magnetic fields, rather than resistance. For this reason, the MR elements in Figure 6 are labeled G1 through G8 (i.e., rather than R1 through R8) to indicate that it is the conductance that varies. Furthermore, the output signals of bridge 600 taken across output nodes 610, 614 are current signals.

[0085]

[0084] The bridge circuit 600 includes a first bridge 604 having MR elements G1 to G4 and a second bridge 609 having MR elements G5 to G8. More specifically, the first bridge 604 includes a first MR element G1, a second MR element G2, a third MR element G3, and a fourth MR element G4. The first MR element G1 is coupled between a current source Icc and a first output node 610. The second MR element G2 is coupled between the current source Icc and a second output node 614. The third MR element G3 is coupled between the second output node 614 and ground. The fourth MR element G4 is coupled between the first output node 610 and ground.

[0086] The second bridge 608 includes a fifth MR element G5, a sixth MR element G6, a seventh MR element G7, and an eighth MR element G8. The fifth MR element G5 is coupled between the current source Icc and the third output node 616, the sixth MR element G6 is coupled between the current source Icc and the fourth output node 618, the seventh MR element G7 is coupled between the fourth output node 618 and ground, and the eighth MR element G8 is coupled between the third output node 616 and ground.

[0087]

[0086] The first MR element G1, the third MR element G3, the sixth MR element G6, and the eighth MR element G8 each have a first magnetic reference direction labeled 620. The second MR element G2, the fourth MR element G4, the fifth MR element G5, and the seventh MR element G7 each have a second magnetic reference direction labeled 622 that is opposite to (i.e., 180 degrees different from) the first magnetic reference direction 620.

[0088]

[0087] In this example, each of the MR elements G1 to G8 is a tunneling magnetoresistive (TMR) element. However, at least some (or all) of the MR elements G1 to G8 may be a giant magnetoresistive (GMR) element or another suitable type of MR element, such as an anisotropic magnetoresistive (AMR) element.

[0089] The output current signal Iout (ie, OUTp-OUTn) of the bridge 600 taken across nodes 610, 614 can be expressed as follows:

[0090]

number

[0091] To use the parallel bridge circuit 600 to detect a magnetic field of interest in a manner immune to stray magnetic fields, the bridges 604, 608 are arranged to detect a differential magnetic field of interest. To this end, the first bridge 604 is arranged to detect a first uniform magnetic field of a first polarity, indicated by arrow 630, and the second bridge 608 is arranged to detect a second uniform magnetic field of a second polarity opposite to the first polarity, indicated by arrow 640, where the first and second uniform magnetic fields are generated by a common magnetic field source and have equal magnitude. An exemplary magnetic field source of a differential magnetic field including uniform magnetic fields of opposite polarities, such as magnetic fields 630, 640, is shown in Figures 7 and 7A.

[0092] Advantageously, bridge circuit 600, with its single output signal across nodes 610, 614, requires only a single signal processing path, unlike bridge circuit 200 of FIG. 2, which requires two signal processing paths, thereby saving power and area.

[0093] Furthermore, the bridge circuit 600 can achieve increased linearity compared to, for example, the bridge configuration 400 (FIG. 4) because, for the same unit cell resistance rating of the MR element, the bridge circuit 600 has half the thermal noise of the bridge circuit 400, thereby increasing the signal-to-noise ratio (SNR) of the sensor.

[0094]

[0092] Because bridge circuit 600 is driven by current Icc and the output signal across nodes 610 and 614 is a current, even further improved linearity is achieved. This power supply and sensing combination of this parallel bridge configuration provides even further improved linearity because each leg of bridge 600 includes parallel-coupled TMR elements (i.e., elements G1 and G5, elements G2 and G6, elements G3 and G7, and elements G4 and G8), and the conductances of such elements in each such pair sum with respect to TMR, which conductance behaves more linearly than the resistance to magnetic field for an individual stack. Thus, the overall response of bridge 600, with its input current source and output current sense, and the summed conductance of each bridge leg, achieves superior linearity compared to, for example, the series-coupled bridge 400 of FIG. 4.

[0095]

[0093] With further reference to Figures 7 and 7A, possible application circuits for use with the parallel bridge circuit 600 of Figure 6 include a current sensor 700 and a rotation sensor 760, respectively.

[0096]

[0094] Figure 7 shows a current sensor 700, which may be the same as or similar to current sensor 300 of Figure 3, and therefore includes a current conductor 750 configured to carry a current indicated by arrow 752. Current 752 generates a magnetic field that is detected by bridge 600 of Figure 6, which includes MR elements G1-G8 arranged and having magnetic reference directions as shown.

[0097]

[0095] MR elements G1-G8 are arranged to differentially detect the magnetic field of interest generated by current 752. In particular, bridge elements G1-G4 are arranged to detect a uniform magnetic field indicated by arrow 630 (which may be the same as or similar to magnetic field 230 or 330), and bridge elements G5-G8 are arranged to detect a uniform magnetic field indicated by arrow 640 (which may be the same as or similar to magnetic field 240 or 340), the uniform magnetic fields 630, 640 having opposite polarities and equal magnitudes.

[0098]

[0096] The electrical connections of the MR elements G1 to G8 are as shown in Figure 6, and the physical configuration of the MR elements can be designed to suit the particular application described above in conjunction with the current sensor 300 of Figure 3.

[0099]

[0097] Figure 7A shows a rotation sensor 760, which may be the same as or similar to rotation sensor 360 of Figure 3A, and thus includes a target 764. Rotation of target 764 generates a magnetic field that is detected by bridge 600 of Figure 6, which includes MR elements G1-G8 arranged as shown and having magnetic reference directions.

[0100]

[0098] MR elements G1-G8 are arranged to differentially detect the generated, rotating, magnetic fields of interest of target 764. In particular, bridge elements G1-G4 are arranged to detect a uniform magnetic field indicated by arrow 630 (which may be the same as or similar to magnetic field 230 or 330), and bridge elements G5-G8 are arranged to detect a uniform magnetic field indicated by arrow 640 (which may be the same as or similar to magnetic field 240 or 340), the uniform magnetic fields 630, 640 having opposite polarities and equal magnitudes.

[0101]

[0099] The electrical connections of the MR elements G1 to G8 are as shown in Figure 6, and the physical configuration of the MR elements can be designed to suit the particular application described above in conjunction with the rotation sensor 360 of Figure 3A.

[0102] 8, a schematic block diagram of an example current sensor 800, such as may form part of the current sensor 300 of FIG. 3 or the current sensor 700 of FIG. 7, may include a bridge circuit as described above, such as the bridge circuit 200 of FIG. 2 or the bridge circuit 600 of FIG. 6. The current sensor 800 includes one or more bridge circuits or bridges 810a, 810b including magnetic field sensing elements. When using the bridge circuit 200 of FIG. 2, each of the bridges 810a, 810b may correspond to the bridge circuits 204, 208, respectively. And, when using the bridge circuit 600 of FIG. 6, the bridge circuit 810b may be omitted, and the parallel-coupled bridges 604, 608 may correspond to the bridge 810a. The sensing elements including the bridge circuits 810a and / or 810b may include, for example, TMR or other magnetoresistive elements.

[0103] The exemplary current sensor 800 has three pins or external connections, including a power supply pin or VCC 801, a VOUT (output signal) pin 802, and a GND (ground) pin 803. The VCC pin 801 is used for the input power supply or supply voltage for the current sensor 800. It will be appreciated that in embodiments where the bridge 810a corresponds to the bridge circuit 600 of FIG. 6, the supply pin 801 can receive a supply current ICC rather than a voltage. A bypass capacitor C BYPASS may be coupled between VCC pin 801 and ground. VCC pin 801 may also be used to program current sensor 800. VOUT pin 802 is used to provide an output signal to current sensor 800 that represents a current (e.g., current 352 in FIG. 3) going into a circuit and system (not shown), and may also be used for programming. It will be appreciated that in embodiments where bridge 810a corresponds to bridge circuit 600 in FIG. 6, output pin 802 may provide a current output signal rather than a voltage output signal. Output load capacitance C Lis coupled between the VOUT pin 802 and ground. The example current sensor 800 may include a first diode D1 coupled between the VCC pin 801 and case ground and a second diode D2 coupled between the VOUT pin 802 and case ground. The driver 820 may provide power connections to the bridges 810a, 810b, which may take the form of a voltage source VCC or a current source Icc.

[0104] The output signals of bridge circuits 810a, 810b are coupled to amplifier 814. Amplifier 814 is configured to generate an amplified signal for coupling to signal recovery circuit 816. In an embodiment, amplifier 814 may be a differential amplifier to provide a subtraction element configured to receive the output signals of bridges 810a, 810b (e.g., here, bridges 810a, 810b correspond to bridges 204, 208 in FIG. 2). A regulator (not shown) may be coupled between supply voltage VCC and ground, as well as to various components and sub-circuits of sensor 800, to adjust the supply voltage.

[0105] To provide appropriate control for the EEPROM and control logic, a programming control circuit 822 is coupled between the VCC pin 801 and the EEPROM and control logic 830. The EEPROM and control logic 830 can determine, erase, and reprogram any application-specific coding using a pulsed voltage. A sensitivity control circuit 824 is coupled to the amplifier 814 and can generate and provide a sensitivity control signal to the amplifier 814 to adjust the amplifier's sensitivity and / or operating voltage. An active temperature compensation circuit 832 can be coupled to the sensitivity control circuit 824, the EEPROM and control logic 830, and an offset control circuit 834. The offset control circuit 834 can generate and provide an offset signal to the push-pull driver 818 (which may be an amplifier) ​​to adjust the driver's sensitivity and / or operating voltage. The active temperature compensation circuit 832 can obtain temperature data from the EEPROM and control logic 830 via the temperature sensor 815 and perform the necessary calculations to compensate for changes in temperature, if necessary. An output clamp circuit 836 may be coupled between the EEPROM and control logic circuit 830 and the driver 818 to limit the output voltage and for diagnostic purposes. For example, if the full output range can be from 0V to 5V for magnetic fields from 0G to 1000G, it may be desirable to use a clamp at 0.5V for any magnetic field below 100G. For example, below 100G, the sensor 800 may be known not to produce a reliable signal. Thus, if the IC output is 0.5V, it is clear that the measurement is not valid and cannot be trusted. Alternatively, clamps at 1V and 4V may be used, and the 0-1V and 4-5V ranges may be used to convey diagnostic information (e.g., 4.5V on the output may indicate a "Hall plate is inoperative," 0.5V may indicate an "undervoltage VCC detected," etc.). An undervoltage detection circuit 826 may function to detect an undervoltage condition of the supply voltage level VCC.Although FIG. 8 illustrates the example current sensor 800 as a primarily analog implementation, it will be appreciated that any suitable current sensor topology may be used, including both digital, analog, and combined digital and analog implementations.

[0106]

[0104] Still referring to Figure 9, a motion / rotation sensor 900 of a type that may form part of rotation sensor 360 of Figure 3A or rotation sensor 760 of Figure 7A may include a bridge circuit as described above, such as the bridge of Figure 2 or the bridge of Figure 6. In the case of bridge circuit 200 of Figure 2, MR element 910 may include bridges 204 and 208. And in the case of bridge circuit 600 of Figure 6, MR element 910 may include the parallel-coupled bridge circuit 600. Sensing element 910 may include, for example, a TMR or other magnetoresistive element.

[0107] In embodiments in which the MR element 910 is configured to provide two output signals (e.g., as in the two-bridge arrangement of FIG. 2), each output signal may be coupled to a respective signal path. For example, a first signal path may include an amplifier 914a and an analog-to-digital converter (ADC) 918a, and a second signal path may include an amplifier 914b and an ADC 918b. Alternatively, in embodiments in which the MR element 910 is configured to provide a single output signal (e.g., as in the parallel-bridge arrangement of FIG. 6), one of the signal paths may be omitted.

[0108] The bridge output signal(s) thus conditioned may be further processed by a digital regulator 920. The regulator 920 may process one or both input signals to determine the speed and / or direction of the target. An output current generator 924 may convert the conditioned signal into a current for transmission to an external system via the VCC connection 901 and the ground connection 903 in a so-called “two-wire” configuration shown. While a two-wire interface is shown, those skilled in the art will appreciate that the sensor 900 may alternatively transmit its output signal to a dedicated output signal pin (not shown) separate from the power connections 901, 903. Additional features of the sensor 900 may include ESD protection 928, a regulator 930, diagnostic circuitry 934, an oscillator 938, and a memory 922 coupled across the sensor pins 901, 903.

[0109]

[0107] While FIG. 9 shows the exemplary rotation sensor 900 as a primarily digital implementation, it will be appreciated that any suitable current sensor topology may be used, including both digital, analog, and combined digital and analog implementations.

[0110] Having described preferred embodiments of the present disclosure, it will now become apparent to those skilled in the art that other embodiments incorporating these concepts may be used. It is felt, therefore, that these embodiments should not be limited to the disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.

Claims

1. a first bridge including a first MR element, a second MR element, a third MR element, and a fourth MR element, wherein the first MR element is coupled between a power supply and a first output node, the second MR element is coupled between the power supply and a second output node, the third MR element is coupled between the second output node and ground, and the fourth MR element is coupled between the first output node and ground; a second bridge including a fifth MR element, a sixth MR element, a seventh MR element, and an eighth MR element, wherein the fifth MR element is coupled between the power supply and a third output node, the sixth MR element is coupled between the power supply and a fourth output node, the seventh MR element is coupled between the fourth output node and ground, and the eighth MR element is coupled between the third output node and ground; Equipped with A magnetic field sensor, wherein the first MR element, the third MR element, the fifth MR element, and the seventh MR element each have a first magnetic reference direction, and the second MR element, the fourth MR element, the sixth MR element, and the eighth MR element each have a second magnetic reference direction opposite to the first magnetic reference direction.

2. 2. The magnetic field sensor of claim 1, wherein the first bridge is positioned to detect a first uniform magnetic field of a first polarity, and the second bridge is positioned to detect a second uniform magnetic field of a second polarity opposite to the first polarity, and the first uniform magnetic field and the second uniform magnetic field are generated by a common magnetic field source and have equal magnitudes.

3. 2. The magnetic field sensor of claim 1, wherein a first electrical signal between the first output node and the second output node represents a first uniform magnetic field, and a second electrical signal between the third output node and the fourth output node represents a second uniform magnetic field.

4. 4. The magnetic field sensor of claim 3, further comprising a subtraction element coupled to receive the first electrical signal and the second electrical signal and configured to generate a subtraction signal representing a difference between the first electrical signal and the second electrical signal, the subtraction signal being independent of stray magnetic fields and representing a magnitude of the first uniform magnetic field.

5. 2. The magnetic field sensor of claim 1, wherein the first output node and the third output node are electrically coupled together, and the second output node and the fourth output node are electrically coupled together.

6. 6. The magnetic field sensor of claim 5, wherein the power supply is a current source and the differential current signal between the first output node and the second output node is independent of stray magnetic fields and represents the magnitude of a first uniform magnetic field.

7. The magnetic field sensor of claim 2 , wherein the first uniform magnetic field and the second uniform magnetic field are generated by current conductors.

8. The magnetic field sensor of claim 7 , wherein the first uniform magnetic field and the second uniform magnetic field are generated by the movement of a ferromagnetic object.

9. 2. The magnetic field sensor of claim 1, wherein each of the first MR element, the second MR element, the third MR element, the fourth MR element, the fifth MR element, the sixth MR element, the seventh MR element, and the eighth MR element comprises a TMR element.

10. 2. The magnetic field sensor of claim 1, wherein the first MR element, the third MR element, the fifth MR element, and the seventh MR element are repinned to have the first magnetic reference direction, or the second MR element, the fourth MR element, the sixth MR element, and the eighth MR element are repinned to have the second magnetic reference direction.

11. a first bridge comprising a first MR element, a second MR element, a third MR element, and a fourth MR element, the first MR element coupled between a power supply and a first output node, the second MR element coupled between the power supply and a second output node, the third MR element coupled between the second output node and ground, and the fourth MR element coupled between the first output node and ground; a second bridge comprising a fifth MR element, a sixth MR element, a seventh MR element, and an eighth MR element, wherein the fifth MR element is coupled between the power supply and a third output node, the sixth MR element is coupled between the power supply and a fourth output node, the seventh MR element is coupled between the fourth output node and ground, and the eighth MR element is coupled between the third output node and ground; and Equipped with A magnetic field sensor, wherein the first bridge is arranged to detect a first uniform magnetic field of a first polarity, and the second bridge is arranged to detect a second uniform magnetic field of a second polarity opposite to the first polarity, the first uniform magnetic field and the second uniform magnetic field being generated by a common magnetic field source and having equal magnitude.

12. 12. The magnetic field sensor of claim 11, wherein the first MR element, the third MR element, the fifth MR element, and the seventh MR element each have a first magnetic reference direction, and the second MR element, the fourth MR element, the sixth MR element, and the eighth MR element each have a second magnetic reference direction opposite to the first magnetic reference direction.

13. 12. The magnetic field sensor of claim 11, wherein a first electrical signal between the first output node and the second output node represents the first uniform magnetic field, and a second electrical signal between the third output node and the fourth output node represents the second uniform magnetic field.

14. 14. The magnetic field sensor of claim 13, further comprising a subtraction element coupled to receive the first electrical signal and the second electrical signal and configured to generate a subtraction signal representing a difference between the first electrical signal and the second electrical signal, the subtraction signal being independent of stray magnetic fields and representing the magnitude of the first uniform magnetic field.

15. The magnetic field sensor of claim 11 , wherein the first output node and the third output node are electrically coupled together, and the second output node and the fourth output node are electrically coupled together.

16. 16. The magnetic field sensor of claim 15, wherein the power supply is a current source and a differential current signal between the first output node and the second output node is independent of stray magnetic fields and represents the magnitude of the first uniform magnetic field.

17. The magnetic field sensor of claim 11 , wherein the first uniform magnetic field and the second uniform magnetic field are generated by current conductors.

18. The magnetic field sensor of claim 11 , wherein the first uniform magnetic field and the second uniform magnetic field are generated by the movement of a ferromagnetic object.

19. 12. The magnetic field sensor of claim 11, wherein each of the first MR element, the second MR element, the third MR element, the fourth MR element, the fifth MR element, the sixth MR element, the seventh MR element, and the eighth MR element comprises a TMR element.

20. 13. The magnetic field sensor of claim 12, wherein the first MR element, the third MR element, the fifth MR element, and the seventh MR element are repinned to have the first magnetic reference direction, or the second MR element, the fourth MR element, the sixth MR element, and the eighth MR element are repinned to have the second magnetic reference direction.

Images