JP7119695B2 - magnetic sensor - Google Patents

Description

The present invention relates to a magnetic sensor, and more particularly to a magnetic sensor capable of preventing detection sensitivity from deteriorating due to a disturbance magnetic field.

Magnetic sensors using magnetoresistive elements are widely used in ammeters, magnetic encoders, and the like. As described in Patent Literature 1, the magnetic sensor may be provided with a magnetic block for concentrating magnetic flux on the magnetoresistive element. For example, in the magnetic sensor described in Patent Document 1, a magnetic block is arranged between two magnetoresistive elements and another two magnetoresistive elements. A structure is described in which magnetic fields of opposite phases are applied to the element. These four magnetoresistive elements constitute a differential bridge circuit, and a vertical magnetic field to be detected is detected based on a differential signal output from the differential bridge circuit.

Japanese Patent No. 5500785

However, in the magnetic sensor described in Patent Document 1, when a disturbance magnetic field such as geomagnetism is applied in the horizontal direction, the disturbance magnetic field in the horizontal direction is applied in phase to the four magnetoresistive elements. There is a problem that the reference point of operation is offset by the magnetic field, which lowers the detection sensitivity of the magnetic field to be detected.

In order to solve this problem, for example, a method of providing another magnetic sensor for detecting the disturbance magnetic field in the horizontal direction and generating a cancellation magnetic field for canceling the disturbance magnetic field based on the output signal of the magnetic sensor is conceivable. requires a separate magnetic sensor for detecting the disturbance magnetic field, which complicates the entire device.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a magnetic sensor capable of preventing reduction in detection sensitivity due to a disturbance magnetic field without adding another magnetic sensor for detecting the disturbance magnetic field.

A magnetic sensor according to the present invention includes first and second magnetoresistive elements to which magnetic fields to be detected are applied in opposite phases, a detection circuit for detecting a difference in resistance value between the first and second magnetoresistive elements, and a magnetic bias circuit for applying an in-phase bias magnetic field to the first and second magnetoresistive elements based on the sum of the resistance values of the first and second magnetoresistive elements.

When a disturbance magnetic field such as geomagnetism is applied to the first and second magnetoresistive elements in the same phase, the sum of the resistance values of the first and second magnetoresistive elements changes accordingly. Focusing on this point, the present invention applies an in-phase bias magnetic field to the first and second magnetoresistive elements based on the sum of the resistance values of the first and second magnetoresistive elements. This makes it possible to prevent the detection sensitivity from being reduced due to the disturbance magnetic field without adding another magnetic sensor for detecting the disturbance magnetic field.

In the present invention, the magnetic bias circuit includes an in-phase coil that generates a bias magnetic field based on the feedback current, a reference resistor, and a feedback current based on the difference between the sum of the resistance values and the resistance value of the reference resistor. It may include an amplifier circuit. According to this, by appropriately setting the resistance value of the reference resistor, it is possible to generate an appropriate feedback current corresponding to the disturbance magnetic field.

The magnetic sensor according to the present invention further includes third and fourth magnetoresistive elements to which magnetic fields to be detected are applied in opposite phases, the first and second magnetoresistive elements are connected in series, and the third and fourth magnetoresistive elements are connected in series. The 4 magnetoresistive elements are connected in series, and the detection circuit detects the difference between the potential at the connection point of the first and second magnetoresistive elements and the potential at the connection point of the third and fourth magnetoresistive elements. The connection point of the first and fourth magnetoresistive elements and one end of the reference resistor are both connected to a common power supply, and the amplifier circuit is connected to the potential of the connection point of the first and fourth magnetoresistive elements, A feedback current may be generated based on the difference from the potential at one end of the reference resistor. According to this, since a full bridge circuit is formed by four magnetoresistive elements, it is possible to obtain higher detection sensitivity.

In the present invention, the magnetic bias circuit may further include a switch that applies a reset potential to one end of the reference resistor. According to this, it is possible to reset the first to fourth magnetoresistive elements to a predetermined initial state of the hysteresis loop before actual measurement.

In the present invention, the resistance value of the reference resistor may be variable. This makes it possible to finely adjust the resistance value of the reference resistor. In this case, the reference resistance may include a magnetically shielded magnetoresistive element. According to this, it becomes possible to cancel the change in the measured value due to the environmental temperature.

In the present invention, the magnetic bias circuit may further include a damping resistor connected in series with the in-phase coil. According to this, it is possible to prevent abnormal oscillation of the magnetic bias circuit.

In the present invention, the magnetic bias circuit may cancel disturbance magnetic fields applied in the same phase to the first and second magnetoresistive elements by a bias magnetic field. According to this, it is possible to detect the magnetic field to be detected in the same environment as when the disturbance magnetic field is substantially zero.

In the present invention, the magnetic bias circuit may keep constant the magnetic fields applied in the same phase to the first and second magnetoresistive elements. According to this, regardless of the direction and strength of the disturbance magnetic field, it is possible to detect the magnetic field to be detected with a substantially constant magnetic bias applied.

A magnetic sensor according to the present invention comprises a sensor chip on which first and second magnetoresistive elements are formed and which has an element formation surface parallel to the sensitivity axis direction of the first and second magnetoresistive elements; It may further include a magnetic block disposed between the first magnetoresistive element and the second magnetoresistive element. According to this, since the magnetic field perpendicular to the element forming surface is split by the magnetic block, it is possible to apply the magnetic field to be detected in opposite phases to the first and second magnetoresistive elements. becomes.

As described above, according to the present invention, it is possible to prevent a decrease in detection sensitivity due to a disturbance magnetic field without adding another magnetic sensor for detecting a disturbance magnetic field.

FIG. 1 is a schematic perspective view for explaining the configuration of main parts of a magnetic sensor 10 according to a preferred embodiment of the invention. FIG. 2 is a schematic top view of the magnetic sensor 10. FIG. FIG. 3 is a schematic cross-sectional view along line AA shown in FIG. FIG. 4 is a circuit diagram of the magnetic bias circuit 30. As shown in FIG. FIG. 5 is a graph showing the relationship between the magnetic field to be detected and the potential difference ΔS between the signals S1 and S2 output from the bridge circuit B for each intensity of the disturbance magnetic field, and shows values when the magnetic bias circuit 30 is not used. there is FIG. 6 is a graph showing the offset characteristics of the magnetoresistive elements MR1-MR4, showing the relationship between the disturbance magnetic field applied in-phase to the magnetoresistive elements MR1-MR4 and the detection sensitivity. FIG. 7 is another graph showing the offset characteristics of the magnetoresistive elements MR1 to MR4, showing the relationship between the combined resistance value of the bridge circuit B and the detection sensitivity. FIG. 8 is a circuit diagram of the magnetic bias circuit 31 according to the first modification. FIG. 9 is a circuit diagram of the magnetic bias circuit 32 according to the second modification. FIG. 10 is a circuit diagram of the magnetic bias circuit 33 according to the third modification. FIG. 11 is a circuit diagram of the magnetic bias circuit 34 according to the fourth modification. FIG. 12 is a circuit diagram of the magnetic bias circuit 35 according to the fifth modification. FIG. 13 is a circuit diagram of the magnetic bias circuit 36 according to the sixth modification. FIG. 14 is a diagram for explaining definitions of in-phase and anti-phase magnetic fields. FIG. 15 is a diagram for explaining definitions of in-phase and anti-phase magnetic fields.

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic perspective view for explaining the configuration of main parts of a magnetic sensor 10 according to a preferred embodiment of the invention. 2 is a schematic top view of the magnetic sensor 10, and FIG. 3 is a schematic cross-sectional view taken along line AA shown in FIG.

As shown in FIGS. 1 to 3, the magnetic sensor 10 according to this embodiment includes a sensor chip 20 and a magnetic block 22 arranged on an element forming surface 21 of the sensor chip 20. FIG. The element forming surface 21 of the sensor chip 20 constitutes an xy plane, and the magnetoresistive elements MR1 and MR3 are formed on one side of the magnetic block 22 when viewed from the z direction, and on the other side of the magnetic block 22 when viewed from the z direction. Magnetoresistive elements MR2 and MR4 are formed on the side.

The sensor chip 20 has a substantially rectangular parallelepiped shape, and four magnetoresistive elements MR1 to MR4 are formed on the element forming surface 21 as described above. The magnetoresistive elements MR1 to MR4 are not particularly limited as long as they are elements whose electric resistance changes according to the direction and strength of the magnetic field. In this embodiment, the sensitivity directions (fixed magnetization directions) of the magnetoresistive elements MR1 to MR4 are all aligned in the direction indicated by the arrow P in FIGS. 2 and 3 (the positive side in the x direction).

The magnetic block 22 is a magnetic collector made of a soft magnetic material with high magnetic permeability such as ferrite. The magnetic block 22 is arranged between the magnetoresistive elements MR1 and MR3 and the magnetoresistive elements MR2 and MR4 in plan view, that is, in the z direction, and has a rectangular parallelepiped shape with the z direction as the longitudinal direction. is doing. As shown in FIG. 3, the magnetic block 22 serves to collect the magnetic flux φ in the z direction and split it to both sides in the x direction. The magnetic flux φ in the z direction is due to the magnetic field to be detected by the magnetic sensor 10 according to this embodiment. As a result, the magnetic fields to be detected are applied to the magnetoresistive elements MR1, MR3 and the magnetoresistive elements MR2, MR4 in opposite phases. The magnetic block 22 may be adhered to the sensor chip 20 using an adhesive or the like, or may be mounted on another mounting substrate (not shown) together with the sensor chip 20 so that the relative positional relationship with the sensor chip 20 is maintained. may be fixed.

The magnetoresistive elements MR1 to MR4 are connected to a detection circuit and a magnetic bias circuit which will be described later. The magnetic bias circuit includes an in-phase coil C shown in FIGS. The in-phase coils C are arranged so as to sandwich the magnetoresistive elements MR1 to MR4 from the x direction. Therefore, when current flows through the in-phase coil C, the resulting magnetic field is applied to the magnetoresistive elements MR1 to MR4 in the same phase. The in-phase coil C may be provided outside the sensor chip 20 or may be formed or mounted on the element forming surface 21 of the sensor chip 20 . Although two in-phase coils C are used in the examples shown in FIGS. 1 and 2, the number of in-phase coils C is not particularly limited in the present invention. Also, the arrangement of the in-phase coil C is not particularly limited as long as the magnetic field generated by the in-phase coil C is applied to the magnetoresistive elements MR1 to MR4 in the same phase. For example, the in-phase coil C does not need to be positioned to sandwich the magnetoresistive elements MR1 to MR4.

FIG. 4 is a circuit diagram of the magnetic bias circuit 30 connected to the magnetoresistive elements MR1-MR4.

As shown in FIG. 4, magnetoresistive elements MR1 to MR4 form a bridge circuit B. As shown in FIG. That is, the magnetoresistive elements MR1 and MR2 are connected in series between the connection point N0 and the ground GND, and the signal S1 is output from the connection point N1 between the magnetoresistive elements MR1 and MR2. Similarly, the magnetoresistive elements MR3 and MR4 are connected in series between the connection point N0 and the ground GND, and the signal S2 is output from the connection point N2 between the magnetoresistive elements MR3 and MR4. The signals S1 and S2 are input to an amplifier circuit A1 forming a detection circuit. The connection point N0 is connected to the power supply VDD through the resistor R1.

As described above, the magnetic fields to be detected are applied to the magnetoresistive elements MR1 and MR3 and the magnetoresistive elements MR2 and MR4 in opposite phases. If the resistance values are lower than those of the elements MR2 and MR4, then S1>S2. Conversely, if the resistance values of the magnetoresistive elements MR1 and MR3 are higher than those of the magnetoresistive elements MR2 and MR4, then S1<S2. The potential difference between the signals S1 and S2 is amplified by the amplifier circuit A1, and as a result the detection signal OUT is generated. A detection signal OUT indicates the strength of the magnetic field to be detected. Thus, the amplifier circuit A1 detects the difference between the resistance values of the magneto-resistive elements MR1 and MR3 and the resistance values of the magneto-resistive elements MR2 and MR4 based on the potential difference between the signals S1 and S2, and based on the detection result, the detection signal Generate OUT.

In this embodiment, a magnetic bias circuit 30 is connected to such a bridge circuit B. As shown in FIG. The magnetic bias circuit 30 includes an amplifier circuit A2 that generates a feedback current I based on the signal S0 and the reference potential Vref, resistors R2 and R3 that generate the reference potential Vref, and an in-phase coil C to which the feedback current I is supplied. . The signal S0 is the potential of the node N0, and its level is determined by the combined resistance value of the bridge circuit B consisting of the magnetoresistive elements MR1 to MR4. The resistors R2 and R3 are connected in series between the power supply VDD and the ground GND, and the reference potential Vref is extracted from the connection point N3 between the two. Resistor R2 has the same resistance value as resistor R1. Also, the resistance value of the resistor R3 is set to the target value of the combined resistance of the bridge circuit B, so that the resistor R3 functions as a reference resistor.

Here, when a disturbance magnetic field such as geomagnetism is generated in the x direction, this disturbance magnetic field is applied to the magnetoresistive elements MR1 to MR4 in the same phase, so that the combined resistance value of the bridge circuit B changes. This is because the magnetoresistive elements MR1 to MR4 change (increase or decrease) in the same direction due to the disturbance magnetic field. Therefore, when a disturbance magnetic field exists, the combined resistance value of the bridge circuit B decreases or increases compared to when the disturbance magnetic field is zero, and as a result, the level of the signal S0 changes. On the other hand, since the level of the reference potential Vref is constant, the amount and direction of the feedback current I generated by the amplifier circuit A2 are linked to the direction and strength of the disturbance magnetic field.

Then, when the feedback current I flows through the in-phase coil C, a bias magnetic field is generated from the in-phase coil C in the direction of canceling the disturbance magnetic field. Since the bias magnetic field generated by the in-phase coil C is applied in-phase to the magnetoresistive elements MR1 to MR4, the disturbance magnetic field is cancelled. As a result, the magnetoresistive elements MR1 to MR4 can detect the magnetic field to be detected in the same environment as when the disturbance magnetic field is substantially zero.

FIG. 5 is a graph showing the relationship between the magnetic field to be detected and the potential difference ΔS between the signals S1 and S2 output from the bridge circuit B for each intensity of the disturbance magnetic field, and shows values when the magnetic bias circuit 30 is not used. there is In FIG. 5, the characteristic B ₀ shows the case where the disturbance magnetic field is zero, and the characteristics B ₁ to B ₃ show the cases where the disturbance magnetic field exists. The intensity of the disturbance magnetic field is B ₁ <B ₂ <B ₃ .

As shown in FIG. 5, when the magnetic bias circuit 30 is not used and the disturbance magnetic field is zero, the amount of change in the potential difference ΔS according to the magnetic field to be detected is large (that is, the detection sensitivity is high), and It can be seen that while the change in the potential difference ΔS is relatively linear, as the disturbance magnetic field increases, the amount of change in the potential difference ΔS corresponding to the magnetic field to be detected decreases, and the linearity also decreases. This is because the operating reference point is offset when a disturbance magnetic field is applied to the magnetoresistive elements MR1 to MR4 in the same phase.

However, since the magnetic sensor 10 according to the present embodiment includes the magnetic bias circuit 30, even if a disturbance magnetic field exists, the disturbance magnetic field is canceled by the in-phase coil C. FIG. As a result, the magnetoresistive elements MR1 to MR4 can detect the magnetic field to be detected in the same environment as when the disturbance magnetic field is almost zero, so it is possible to ensure higher detection sensitivity than in the past. . Moreover, in the magnetic sensor 10 according to the present embodiment, since the magnetoresistive elements MR1 to MR4 themselves function as magnetic sensors for detecting disturbance magnetic fields, there is no need to separately use a dedicated magnetic sensor for detecting disturbance magnetic fields. do not have.

On the other hand, the actually manufactured magnetoresistive elements MR1 to MR4 do not always have ideal characteristics, and in some cases, the characteristics are offset from the beginning. FIG. 6 is a graph showing an example of the offset characteristics of the magnetoresistive elements MR1 to MR4, showing the relationship between the disturbance magnetic field applied in phase to the magnetoresistive elements MR1 to MR4 and the detection sensitivity. The horizontal axis indicates the strength of the disturbance magnetic field in the x direction, meaning that the strength of the disturbance magnetic field in the +x direction increases as it moves away from zero in the + direction, and the disturbance magnetic field in the −x direction increases as it moves away from zero in the − direction. It means that the intensity of is strong. The detection sensitivity is defined by the amount of change in the potential difference ΔS with respect to the unit amount of change in the magnetic field to be detected. In the example shown in FIG. 6, higher detection sensitivity is obtained in an environment where a predetermined disturbance magnetic field H exists in the +x direction than in the case where the disturbance magnetic field is zero. This phenomenon is caused by the offset of the magnetoresistive elements MR1 to MR4.

When such an offset exists, instead of completely canceling the disturbance magnetic field by the in-phase coil C, the bias magnetic field by the in-phase coil C applies a constant magnetic bias to the magnetoresistive elements MR1 to MR4. I don't mind. This can be realized by offsetting the resistance value of the resistor R3, which is the reference resistor. Specifically, as shown in FIG. 7, the horizontal axis of FIG. 6 is replaced with the combined resistance value of the bridge circuit B, and the resistance value of the resistor R3 is set to the same resistance value as the combined resistance value that provides the desired detection sensitivity. do it. In the example shown in FIG. 7, the highest detection sensitivity can be obtained by setting the resistance value of the resistor R3 not to the resistance value R0 when the disturbance magnetic field is _zero but to the resistance value RH when the disturbance magnetic field _H exists. Obtainable.

The conversion from the horizontal axis of FIG. 6 to the horizontal axis of FIG. 7, that is, the conversion from the disturbance magnetic field to the combined resistance value may be performed using a known relational expression or graph. It may be done by actually measuring the combined resistance value for each direction.

As described above, the magnetic sensor 10 according to the present embodiment includes the magnetic bias circuit 30 that keeps the magnetic field applied in the same phase to the magnetoresistive elements MR1 to MR4 constant. In addition, it is also possible to apply a constant magnetic bias to the magnetoresistive elements MR1 to MR4 so as to obtain desired detection sensitivity. This makes it possible to prevent the detection sensitivity from being reduced due to the disturbance magnetic field without adding another magnetic sensor for detecting the disturbance magnetic field.

Several modifications of the magnetic bias circuit are described below.

FIG. 8 is a circuit diagram of the magnetic bias circuit 31 according to the first modification.

The magnetic bias circuit 31 shown in FIG. 8 differs from the magnetic bias circuit 30 shown in FIG. 4 in that the electrical polarities are reversed. That is, the connection relationship between the bridge circuit B and the resistor R1 is opposite to that of the magnetic bias circuit 30 shown in FIG. 4, and the connection relationship between the resistor R2 and the resistor R3 is opposite to that of the magnetic bias circuit 30 shown in FIG. is. As exemplified by the magnetic bias circuit 31 shown in FIG. 8, the electrical polarity of the magnetic bias circuit is not particularly limited in the present invention.

FIG. 9 is a circuit diagram of the magnetic bias circuit 32 according to the second modification.

The magnetic bias circuit 32 shown in FIG. 9 differs from the magnetic bias circuit 30 shown in FIG. 4 in that the resistor R3 is composed of a series connection of a fixed resistor R31 and a variable resistor R32. By using such a variable resistor R32, it becomes possible to easily adjust the resistance value of the resistor R3. In particular, if the resistance values of the fixed resistor R31 and the variable resistor R32 are distributed such that most of the resistance value of the resistor R3 consists of the resistance component of the fixed resistor R31, fine adjustment becomes easier. For example, if the approximate combined resistance value RB of the bridge circuit _B is known, by setting the resistance value of the fixed resistor _R31 to a value slightly lower than RB, the resistance value of the resistor R3 is calculated using the variable resistor R32. can be adjusted with high precision.

In the example shown in FIG. 9, the resistor R3 is configured by a series connection of the fixed resistor R31 and the variable resistor R32, but the resistor R3 may be configured by a parallel connection of the fixed resistor R31 and the variable resistor R32. The resistor R3 may be composed only of the variable resistor R32. Also, a plurality of variable resistors R32 may be used.

Furthermore, a magnetically shielded magnetoresistive element may be used as the fixed resistor R31. According to this, changes in the resistance values of the magnetoresistive elements MR1 to MR4 according to the ambient temperature are also reflected in the fixed resistor R31, so that the temperature characteristics can be kept substantially constant. However, the magnetoresistive element used as the fixed resistor R31 must be magnetically shielded in order to prevent the resistance value from changing due to the magnetic field. Also. The variable resistor R32 may be a magnetically shielded magnetoresistive element.

FIG. 10 is a circuit diagram of the magnetic bias circuit 33 according to the third modification.

The magnetic bias circuit 33 shown in FIG. 10 differs from the magnetic bias circuit 30 shown in FIG. 4 in that a damping resistor R4 is connected in series with the in-phase coil C. By connecting such a damping resistor R4 in series with the in-phase coil C, abnormal oscillation of the feedback current I flowing through the in-phase coil C can be prevented.

FIG. 11 is a circuit diagram of the magnetic bias circuit 34 according to the fourth modification.

A magnetic bias circuit 34 according to a fourth modification shown in FIG. 11 is different from the magnetic bias circuit 30 shown in FIG. 4 in that a switch SW is connected in parallel with the resistor R3. If such a switch SW is provided, the reference potential Vref can be temporarily fixed to ground GND, which is the reset potential, by temporarily turning on the switch SW. When the reference potential Vref is fixed to the ground GND, a large feedback current I flows through the in-phase coil C so that the combined resistance value of the bridge circuit B is minimized. It is possible to reset the first to fourth magnetoresistive elements MR1 to MR4 to a predetermined initial state of the hysteresis loop.

FIG. 12 is a circuit diagram of the magnetic bias circuit 35 according to the fifth modification.

A magnetic bias circuit 35 according to a fifth modification shown in FIG. 12 is different from the magnetic bias circuit 30 shown in FIG. 4 in that a switch SW is connected in parallel with the resistor R2. By providing such a switch SW, the reference potential Vref can be temporarily fixed to the power supply VDD, which is the reset potential, by temporarily turning on the switch SW. When the reference potential Vref is fixed to the power supply VDD, a large feedback current I flows through the in-phase coil C so that the combined resistance value of the bridge circuit B is maximized. It is possible to reset the first to fourth magnetoresistive elements MR1 to MR4 to a predetermined initial state of the hysteresis loop.

FIG. 13 is a circuit diagram of the magnetic bias circuit 36 according to the sixth modification.

A magnetic bias circuit 36 according to a sixth modification shown in FIG. 13 differs from the magnetic bias circuit 32 shown in FIG. 9 in that a switch SW is connected in parallel with a variable resistor R32. By providing such a switch SW, by temporarily turning on the switch SW, the reference potential Vref can be fixed at a reset potential that is significantly lower than that during normal operation. When the reference potential Vref is fixed at a reset potential significantly lower than that during normal operation, a large feedback current I flows through the common-mode coil C so that the combined resistance value of the bridge circuit B becomes sufficiently small. By performing the operation before the actual measurement, it becomes possible to reset the first to fourth magnetoresistive elements MR1 to MR4 to a predetermined initial state of the hysteresis loop.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention. Needless to say, it is included within the scope.

For example, in the above embodiment, the bridge circuit B is configured using four magnetoresistive elements MR1 to MR4, but the number of magnetoresistive elements used in the present invention is not limited to this. Therefore, the bridge circuit B may be constructed by using two magnetoresistive elements (for example, the magnetoresistive elements MR1 and MR2) and connecting them in a half bridge.

Whether the magnetic field is "in-phase" or "anti-phase" is defined in relation to the sensitivity direction (fixed magnetization direction) of the magnetoresistive element, and is not determined solely by the direction of the magnetic field. For example, as shown in FIG. 14, if the magnetoresistive elements MR1 and MR2 have the same fixed magnetization direction (the direction indicated by the arrow P), the magnetoresistive elements MR1 and If the magnetic fields are in the same direction with respect to MR2, they are in "in-phase". On the other hand, as shown in FIG. 15, if the fixed magnetization directions of the magnetoresistive elements MR1 and MR2 (the direction indicated by the arrow P) are opposite to each other, the magnetoresistive element If the magnetic fields for MR1 and MR2 are directed in opposite directions, they are in "in-phase", and if the magnetic fields are in the same direction for the magnetoresistive elements MR1 and MR2, they are in "opposite phase".

10 magnetic sensor 20 sensor chip 21 element forming surface 22 magnetic material blocks 30 to 36 magnetic bias circuits A1 and A2 amplifier circuit B bridge circuit C in-phase coil I feedback currents MR1 to MR4 magnetoresistive elements N0 to N3 connection points R1 to R3 resistor R31 Fixed resistor R32 Variable resistor R4 Damping resistor SW Switch φ Magnetic flux

Claims (10)

first and second magnetoresistive elements to which magnetic fields to be detected are applied in opposite phases;
a detection circuit for detecting a difference in resistance between the first and second magnetoresistive elements;
a magnetic bias circuit that applies an in-phase bias magnetic field to the first and second magnetoresistive elements based on the sum of the resistance values of the first and second magnetoresistive elements. . The magnetic bias circuit generates the feedback current based on an in-phase coil that generates the bias magnetic field based on the feedback current, a reference resistor, and a difference between the sum of the resistance values and the resistance value of the reference resistor. 2. The magnetic sensor of claim 1, further comprising an amplifier circuit. Further comprising third and fourth magnetoresistive elements to which the magnetic fields to be detected are applied in opposite phases to each other,
the first and second magnetoresistive elements are connected in series;
the third and fourth magnetoresistive elements are connected in series;
The detection circuit detects a difference between a potential at a connection point of the first and second magnetoresistive elements and a potential at a connection point of the third and fourth magnetoresistive elements,
A connection point between the first and fourth magnetoresistive elements and one end of the reference resistor are both connected to a common power supply,
3. The amplifier circuit generates the feedback current based on a difference between a potential at a connection point of the first and fourth magnetoresistive elements and a potential at the one end of the reference resistor. 3. The magnetic sensor according to 2. 4. The magnetic sensor according to claim 3, wherein said magnetic bias circuit further includes a switch that applies a reset potential to said one end of said reference resistor. 5. The magnetic sensor according to claim 2, wherein the resistance value of said reference resistor is variable. 6. The magnetic sensor of claim 5, wherein the reference resistance includes a magnetically shielded magnetoresistive element. 7. The magnetic sensor according to claim 2, wherein said magnetic bias circuit further includes a damping resistor connected in series with said in-phase coil. 8. The magnetic bias circuit according to any one of claims 1 to 7, wherein the magnetic bias circuit cancels, with the bias magnetic field, disturbance magnetic fields applied in phase to the first and second magnetoresistive elements. magnetic sensor. 8. The magnetic sensor according to any one of claims 1 to 7, wherein the magnetic bias circuit keeps constant the magnetic fields applied in phase to the first and second magnetoresistive elements. a sensor chip on which the first and second magnetoresistive elements are formed and which has an element formation surface parallel to the sensitivity axis direction of the first and second magnetoresistive elements;
10. The device according to any one of claims 1 to 9, further comprising a magnetic block arranged on the element forming surface and positioned between the first magnetoresistive element and the second magnetoresistive element. 1. The magnetic sensor according to item 1.

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