JP2019219294A - Magnetic sensor - Google Patents

Abstract

To provide a magnetic sensor with which it is possible to prevent or reduce contraction of a dynamic range due to a disturbance magnetic field, without adding another magnetic sensor for detecting the disturbance magnetic field.SOLUTION: A magnetic sensor comprises: magnetoresistive elements MR1, MR2 to which a magnetic field to be detected is applied in a mutually reverse phase; a feedback circuit 31 for applying an anti-phase canceling magnetic field to the magnetoresistive elements MR1, MR2 on the basis of a difference in resistance values of the magnetoresistive elements MR1, MR2; and a magnetic bias circuit 32 for applying an in-phase bias magnetic field to the magnetoresistive elements MR1, MR2 on the basis of a sum of resistance values of the magnetoresistive elements MR1, MR2. Thus, it is possible to prevent or reduce contraction of a dynamic range due to a disturbance magnetic field, without adding another magnetic sensor for detecting the disturbance magnetic field. Since what is called closed-loop control is performed by the feedback circuit 31, it is possible to maintain sensitivity of detecting the magnetic field almost constant.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a magnetic sensor, and more particularly, to a magnetic sensor capable of preventing or reducing a dynamic range due to a disturbance magnetic field.

  Magnetic sensors using magnetoresistive elements are widely used in ammeters, magnetic encoders, and the like. The magnetic sensor described in Patent Literature 1 includes a feedback coil (113) that applies a cancel magnetic field to a magnetoresistive element by a feedback current, and performs closed loop control. The offset of the magnetic sensor described in Patent Document 1 can be adjusted by the adjustment circuit (13).

Japanese Patent No. 5891516

  However, in the magnetic sensor described in Patent Literature 1, since the adjustment of the offset and the sensitivity by the adjustment circuit is performed at the manufacturing stage, when the disturbance magnetic field applied to the magnetoresistive element in the same phase during actual use changes, There is a problem that the operation reference point is offset, thereby reducing the dynamic range.

  In order to solve this problem, for example, another magnetic sensor for detecting a disturbance magnetic field is provided, and a method of generating a cancel magnetic field that cancels the disturbance magnetic field based on the output signal is considered. Since another magnetic sensor for detecting a disturbance magnetic field is required, the entire apparatus is complicated.

  Accordingly, an object of the present invention is to provide a magnetic sensor capable of preventing or reducing the reduction of the dynamic range due to a disturbance magnetic field without adding another magnetic sensor for detecting a disturbance magnetic field.

  According to the magnetic sensor of the present invention, the first and second magnetoresistive elements to which the magnetic field to be detected is applied in opposite phases to each other, and the first and second magnetoresistive elements based on a difference in resistance between the first and second magnetoresistive elements. A feedback circuit for applying a cancel magnetic field of opposite phase to the second magnetoresistive element, and a bias magnetic field having the same phase for the first and second magnetoresistive elements based on the sum of the resistance values of the first and second magnetoresistive elements. And a magnetic bias circuit that provides the following.

  When a disturbance magnetic field such as terrestrial magnetism is applied to the first and second magnetoresistance elements in the same phase, the sum of the resistance values of the first and second magnetoresistance elements changes accordingly. The present invention pays attention to this point, and 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 or reduce the reduction of the dynamic range due to the disturbance magnetic field without adding another magnetic sensor for detecting the disturbance magnetic field. In addition, in the present invention, since a cancel magnetic field of opposite phase is given to the first and second magnetoresistive elements based on the difference between the resistance values of the first and second magnetoresistive elements, a so-called closed loop Control is performed, which makes it possible to maintain the magnetic field detection sensitivity substantially constant.

  In the present invention, the feedback circuit includes a first amplifier circuit that generates a first feedback current based on the difference between the resistance values, and a negative-phase coil that generates a cancel magnetic field based on the first feedback current. It may be something. According to this, by appropriately setting the gain and the phase, the closed loop control can be performed correctly, and the detection sensitivity of the magnetic field can be maintained substantially constant.

  In the present invention, the magnetic bias circuit includes: a reference resistor; a second amplifier circuit that generates a second feedback current based on a difference between a sum of the resistance values and a resistance value of the reference resistor; And an in-phase coil for generating a bias magnetic field based on the above. According to this, by appropriately setting the resistance value of the reference resistor, it is possible to generate an appropriate feedback current according to the disturbance magnetic field.

  The magnetic sensor according to the present invention further includes third and fourth magnetoresistive elements to which detection target magnetic fields are applied in opposite phases, wherein the first and second magnetoresistive elements are connected in series, and the third and fourth magnetoresistive elements are connected in series. 4 are connected in series, and the first amplifier circuit is configured to determine the potential of the connection point of the first and second magnetoresistance elements and the potential of the connection point of the third and fourth magnetoresistance elements. The difference is detected, and 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 second amplifier circuit is connected to the first and fourth magnetoresistive elements. The second feedback current may be generated based on the difference between the potential at the connection point and the potential at one end of the reference resistor. According to this, since a full bridge circuit is formed by the four magnetoresistive elements, a higher SN ratio can be obtained.

  In the present invention, the magnetic bias circuit may further include a switch for applying 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 performing the actual measurement.

  In the present invention, the resistance value of the reference resistor may be variable. According to this, the resistance value of the reference resistor can be finely adjusted. In this case, the reference resistance may include a magnetically shielded magnetoresistive element. According to this, it is 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 a disturbance magnetic field applied to the first and second magnetic resistance elements in the same phase by a bias magnetic field. According to this, it is possible to detect the detection target magnetic field in the same environment as when the disturbance magnetic field is substantially zero.

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

  A magnetic sensor according to the present invention includes a sensor chip having first and second magnetoresistive elements formed thereon and having an element forming surface parallel to a sensitivity axis direction of the first and second magnetoresistive elements, and a sensor chip on the element forming surface. It may be further provided with a magnetic block disposed and located between the first magnetoresistive element and the second magnetoresistive element. According to this, since the magnetic field in the direction perpendicular to the element formation surface is split by the magnetic block, the detection target magnetic field can be applied to the first and second magnetoresistive elements in opposite phases. It becomes.

  In this case, the negative phase coil may be formed on the sensor chip so as to overlap the first and second magnetoresistive elements. According to this, it is possible to reduce the number of parts.

  According to the present invention, it is possible to prevent or reduce the reduction of the dynamic range due to the disturbance magnetic field without adding another magnetic sensor for detecting the disturbance magnetic field while realizing the closed-loop control.

FIG. 1 is a schematic perspective view for explaining a configuration of a main part of a magnetic sensor 10 according to a preferred embodiment of the present invention. FIG. 2 is a schematic top view of the magnetic sensor 10. FIG. 3 is a schematic sectional view taken along line AA shown in FIG. FIG. 4 is a circuit diagram of the feedback circuit 31 and the magnetic bias circuit 32 connected to the magnetoresistive elements MR1 to MR4. FIG. 5 is a graph showing the relationship between the detection target magnetic field and the detection voltage Vout. FIG. 6 is a circuit diagram of the magnetic bias circuit 32a according to the first modification. FIG. 7 is a circuit diagram of a magnetic bias circuit 32b according to a second modification. FIG. 8 is a circuit diagram of a magnetic bias circuit 32c according to the third modification. FIG. 9 is a circuit diagram of a magnetic bias circuit 32d according to a fourth modification. FIG. 10 is a circuit diagram of a magnetic bias circuit 32e according to a fifth modification. FIG. 11 is a circuit diagram of a magnetic bias circuit 32f according to a sixth modification. FIG. 12 is a diagram for explaining the definition of the in-phase and the out-of-phase of the magnetic field. FIG. 13 is a diagram for explaining the definitions of the in-phase and out-of-phase magnetic fields.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

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

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

  The sensor chip 20 has a substantially rectangular parallelepiped shape, and as described above, the four magnetoresistive elements MR1 to MR4 are formed on the element forming surface 21. The magnetoresistive elements MR1 to MR4 are not particularly limited as long as the electric resistance changes according to the direction and strength of the magnetic field. In the present 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).

  Further, the sensor chip 20 is formed with a negative-phase coil C1 so as to overlap the magnetoresistive elements MR1 to MR4 when viewed from the z direction. When the first feedback current I1 flows through the negative-phase coil C1, the first feedback current I1 flows in opposite directions to a portion overlapping the magnetoresistive elements MR1 and MR3 and a portion overlapping the magnetoresistive elements MR2 and MR4. . Thereby, as shown in FIG. 3, the cancel magnetic field φ1 applied to the magnetoresistive elements MR1 and MR3 and the cancel magnetic field φ2 applied to the magnetoresistive elements MR2 and MR4 have opposite phases. In the example illustrated in FIGS. 1 to 3, the negative-phase coil C1 is configured by a one-turn conductor pattern. However, by winding the negative-phase coil C1 a plurality of turns, a plurality of conductors configuring the negative-phase coil C1 are formed. The pattern may overlap with the magnetoresistive elements MR1 to MR4. Further, as long as cancel magnetic fields φ1 and φ2 having opposite phases can be applied to magnetoresistive elements MR1 to MR4, magnetoresistive elements MR1 to MR4 and negative phase coil C1 do not have to overlap. Further, it is not essential to form the negative-phase coil C1 on the sensor chip 20, and the negative-phase coil C1 may be provided outside the sensor chip 20.

  The magnetic block 22 is a magnetic collector made of a soft magnetic material having high magnetic permeability such as ferrite. The magnetic block 22 is disposed between the magnetoresistive elements MR1 and MR3 and the magnetoresistive elements MR2 and MR4 in plan view, that is, when viewed from the z direction, and has a rectangular parallelepiped shape whose longitudinal direction is the z direction. are doing. As shown in FIG. 3, the magnetic block 22 collects the magnetic field φ to be detected in the z direction and plays a role of splitting the magnetic field φ on both sides in the x direction. The detection target magnetic field φ in the z direction is based on the detection target magnetic field to be detected by the magnetic sensor 10 according to the present embodiment. As a result, the magnetic field to be detected is applied to the magnetoresistive elements MR1 and MR3 and the magnetoresistive elements MR2 and MR4 in mutually 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, and a relative positional relationship with the sensor chip 20 may be provided. May be fixed.

  The magnetoresistive elements MR1 to MR4 are connected to a feedback circuit 31 and a magnetic bias circuit 32 described later. The feedback circuit 31 includes the above-described negative-phase coil C1. On the other hand, the magnetic bias circuit 32 includes the in-phase coil C2 shown in FIGS. The in-phase coil C2 is arranged so as to sandwich the magnetoresistive elements MR1 to MR4 from the x direction. Therefore, when a current flows through the in-phase coil C2, the magnetic field generated by the current is applied to the magnetoresistive elements MR1 to MR4 in the same phase. The in-phase coil C2 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. 1 and 2, two in-phase coils C2 are used, but the number of in-phase coils C2 is not particularly limited in the present invention. The arrangement of the in-phase coil C2 is not particularly limited as long as the magnetic field generated by the in-phase coil C2 is applied to the magneto-resistance elements MR1 to MR4 in the same phase. For example, the in-phase coil C2 does not have to be at a position sandwiching the magnetoresistive elements MR1 to MR4.

  FIG. 4 is a circuit diagram of the feedback circuit 31 and the magnetic bias circuit 32 connected to the magnetoresistive elements MR1 to MR4.

  As shown in FIG. 4, the magnetoresistive elements MR1 to MR4 constitute a bridge circuit B. 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 magnetoresistance 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 a signal S2 is output from a connection point N2 between the magnetoresistance elements MR3 and MR4. The signals S1 and S2 are input to a first amplifier circuit A1 that forms a feedback circuit 31, and thereby a first feedback current I1 is generated based on a potential difference between the signals S1 and S2. The connection point N0 is connected to the power supply VDD via the resistor R1.

  As described above, since the detection target magnetic fields are applied to the magnetoresistive elements MR1 and MR3 and the magnetoresistive elements MR2 and MR4 in opposite phases, for example, the resistance values of the magnetoresistive elements MR1 and MR3 are If the resistance value is lower than the resistance values of the elements MR2 and MR4, S1> S2. Conversely, if the resistance value of the magnetoresistive elements MR1 and MR3 is higher than the resistance values of the magnetoresistive elements MR2 and MR4, S1 <S2. Due to the potential difference between the signals S1 and S2, a first feedback current I1 flows from the first amplifier circuit A1 to the negative-phase coil C1.

  As described above, the negative-phase coil C1 is laid out so as to apply the negative-phase cancel magnetic fields φ1 and φ2 to the magnetoresistance elements MR1 and MR3 and the magnetoresistance elements MR2 and MR4. Thus, when the first feedback current I1 flows through the negative-phase coil C1, the detection target magnetic field φ is canceled, and the negative-phase magnetic field applied to the magnetoresistive elements MR1 and MR3 and the magnetoresistive elements MR2 and MR4 is detected. It becomes almost zero regardless of the magnetic field φ. Then, the first feedback current I1 is current-voltage converted by the output resistor Ro, and a detection voltage Vout proportional to the strength of the detection target magnetic field φ is generated. By such closed loop control, the detection sensitivity of the magnetic sensor 10 is kept almost constant.

  In the present embodiment, the magnetic bias circuit 32 is further connected to such a bridge circuit B. The magnetic bias circuit 32 includes a second amplifier circuit A2 that generates a second feedback current I2 based on the signal S0 and the reference potential Vref, resistors R2 and R3 that generate a reference potential Vref, and a second feedback current I2. Is supplied from the in-phase coil C2. The signal S0 is the potential of the connection point N0, and its level is determined by the combined resistance value of the bridge circuit B including 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 a reference potential Vref is extracted from a connection point N3 between the two. The resistor R2 has the same resistance value as the resistor R1. The resistance value of the resistor R3 is set to the target value of the combined resistance of the bridge circuit B, whereby the resistor R3 functions as a reference resistor.

  Here, when a disturbance magnetic field such as terrestrial magnetism is generated in the x direction, the 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 directions in which the resistance values of the magnetoresistive elements MR1 to MR4 change (increase / decrease) due to the disturbance magnetic field are the same. Therefore, when a disturbance magnetic field exists, the combined resistance value of the bridge circuit B decreases or increases as compared with the case where 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 second feedback current I2 generated by the second amplifier circuit A2 are linked to the direction and intensity of the disturbance magnetic field. Become.

  When the second feedback current I2 flows through the in-phase coil C2, a bias magnetic field is generated from the in-phase coil C2 in a direction to cancel the disturbance magnetic field. Since the bias magnetic field generated by the in-phase coil C2 is applied to the magneto-resistive elements MR1 to MR4 in the same phase, the disturbance magnetic field is canceled. Thus, 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 detection target magnetic field and the detection voltage Vout. The characteristic H0 shown in FIG. 5 shows the characteristic when the disturbance magnetic field is zero, and the characteristics H1, H2, and H3 show the characteristic when the disturbance magnetic field exists. Here, the intensity of the disturbance magnetic field increases in the order of the characteristics H1, H2, and H3 (H1 <H2 <H3).

  As shown by the characteristic H0 in FIG. 5, when there is no disturbance magnetic field, the value of the detection voltage Vout when the magnetic field to be detected is zero is almost zero. On the other hand, when a disturbance magnetic field exists, an offset occurs in the detection voltage Vout when the detection target magnetic field is zero, and the offset level becomes larger as the disturbance magnetic field becomes stronger. As a result, the stronger the disturbance magnetic field, the larger the measurement error and the smaller the dynamic range.

  However, since the magnetic sensor 10 according to the present embodiment includes the magnetic bias circuit 32, even when a disturbance magnetic field exists, the disturbance magnetic field is canceled by the in-phase coil C2. Accordingly, 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 that the measurement error due to the disturbance magnetic field is canceled and a sufficient dynamic range is obtained. Can be secured. 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 a disturbance magnetic field, it is necessary to separately use a dedicated magnetic sensor for detecting a disturbance magnetic field. Absent.

  Incidentally, the actually manufactured magnetoresistive elements MR1 to MR4 do not always have ideal characteristics. In some cases, the characteristics are offset from the beginning. When such an offset exists, the magnetic field is not completely canceled by the in-phase coil C2, but a constant magnetic bias is applied to the magnetoresistive elements MR1 to MR4 by the bias magnetic field by the in-phase coil C2. It does not matter. This can be realized by offsetting the resistance value of the resistance R3, which is the reference resistance.

  As described above, since the magnetic sensor 10 according to the present embodiment includes the magnetic bias circuit 32 that keeps the magnetic field applied to the magnetoresistive elements MR1 to MR4 in the same phase, the disturbance magnetic field is canceled. In addition to this, it is also possible to apply a constant magnetic bias to the magnetoresistive elements MR1 to MR4 so that desired characteristics can be obtained. This makes it possible to prevent or reduce the reduction of the dynamic range due to the disturbance magnetic field without adding another magnetic sensor for detecting the disturbance magnetic field. In addition, since the feedback circuit 31 for providing the canceling magnetic field of the opposite phase to the magnetoresistive elements MR1 and MR3 and the magnetoresistive elements MR2 and MR4 is provided, the detection sensitivity of the magnetic sensor 10 is made substantially constant by the closed loop control. It is also possible to keep.

  Hereinafter, some modified examples of the magnetic bias circuit will be described.

  FIG. 6 is a circuit diagram of the magnetic bias circuit 32a according to the first modification.

  The magnetic bias circuit 32a according to the first modification shown in FIG. 6 is different from the magnetic bias circuit 32 shown in FIG. 4 in that the electrical polarity is inverted. That is, the connection relationship between the bridge circuit B and the resistor R1 is opposite to that of the magnetic bias circuit 32 shown in FIG. 4, and the connection relationship between the resistors R2 and R3 is opposite to that of the magnetic bias circuit 32 shown in FIG. It is. As exemplified by the magnetic bias circuit 32a shown in FIG. 6, in the present invention, the electrical polarity of the magnetic bias circuit is not particularly limited.

  FIG. 7 is a circuit diagram of a magnetic bias circuit 32b according to a second modification.

The magnetic bias circuit 32b according to the second modification shown in FIG. 7 differs from the magnetic bias circuit 32 shown in FIG. 4 in that the resistor R3 is configured by connecting a fixed resistor R31 and a variable resistor R32 in series. I have. By using such a variable resistor R32, the resistance value of the resistor R3 can be easily adjusted. In particular, if the resistance values of the fixed resistor R31 and the variable resistor R32 are distributed so that most of the resistance value of the resistor R3 is made up of the resistance component of the fixed resistor R31, fine adjustment can be facilitated. For example, if the approximate combined resistance value R _B is a known bridge circuit B, by setting the resistance value of the fixed resistor R31 to a value slightly lower than R _B, the resistance value of the resistor R3 using a variable resistor R32 Can be adjusted with high accuracy.

  In the example shown in FIG. 7, the resistor R3 is configured by connecting the fixed resistor R31 and the variable resistor R32 in series. However, the resistor R3 may be configured by connecting the fixed resistor R31 and the variable resistor R32 in parallel. The resistor R3 may be constituted only by the variable resistor R32. Further, a plurality of variable resistors R32 may be used.

  Further, a magnetically shielded magnetoresistive element may be used as the fixed resistor R31. According to this, a change in the resistance value of each of the magnetoresistive elements MR1 to MR4 according to the environmental temperature is also reflected on the fixed resistor R31, so that the temperature characteristics can be kept almost constant. However, the magnetoresistive element used as the fixed resistor R31 needs to be magnetically shielded to prevent a change in resistance value due to a magnetic field. Also. The variable resistor R32 may be a magnetically shielded magnetoresistive element.

  FIG. 8 is a circuit diagram of a magnetic bias circuit 32c according to the third modification.

  The magnetic bias circuit 32c according to the third modified example shown in FIG. 8 differs from the magnetic bias circuit 32 shown in FIG. 4 in that a damping resistor R4 is connected in series to the in-phase coil C2. If such a damping resistor R4 is connected in series to the in-phase coil C2, it is possible to prevent abnormal oscillation of the second feedback current I2 flowing through the in-phase coil C2.

  FIG. 9 is a circuit diagram of a magnetic bias circuit 32d according to a fourth modification.

  The magnetic bias circuit 32d according to the fourth modification shown in FIG. 9 differs from the magnetic bias circuit 32 shown in FIG. 4 in that a switch SW is connected in parallel to the resistor R3. If such a switch SW is provided, the reference potential Vref can be temporarily fixed to the 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 I2 flows through the common-mode coil C2 so that the combined resistance value of the bridge circuit B is minimized. The first to fourth magnetoresistive elements can be reset to a predetermined initial state of the hysteresis loop.

  FIG. 10 is a circuit diagram of a magnetic bias circuit 32e according to a fifth modification.

  The magnetic bias circuit 32e according to the fifth modification shown in FIG. 10 differs from the magnetic bias circuit 32d according to the fourth modification shown in FIG. 9 in that a switch SW is connected in parallel to the resistor R2. are doing. If such a switch SW is provided, the reference potential Vref can be temporarily fixed to the power supply VDD which is a 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 I2 flows through the common-mode coil C2 so that the combined resistance value of the bridge circuit B is maximized. The first to fourth magnetoresistive elements can be reset to a predetermined initial state of the hysteresis loop.

  FIG. 11 is a circuit diagram of a magnetic bias circuit 32f according to a sixth modification.

  The magnetic bias circuit 32f according to the sixth modification shown in FIG. 11 differs from the magnetic bias circuit 32b shown in FIG. 7 in that a switch SW is connected in parallel to the variable resistor R32. If such a switch SW is provided, the reference potential Vref can be fixed to a reset potential that is significantly lower than that in the normal operation by turning on the switch SW temporarily. When the reference potential Vref is fixed to a reset potential that is significantly lower than that during normal operation, a large feedback current I2 flows through the common-mode coil C2 so that the combined resistance value of the bridge circuit B becomes sufficiently small. By performing the operation before the actual measurement, the first to fourth magnetoresistive elements can be reset to a predetermined initial state of the hysteresis loop.

  As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It goes without saying that they are included in the range.

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

  Whether the magnetic field is “in phase” or “out of 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. 12, if the fixed magnetization directions (directions indicated by arrows P) of the magnetoresistive elements MR1 and MR2 are the same as each other, as shown in FIG. If the magnetic fields are in the same direction with respect to MR2, the phases are "in-phase". On the other hand, as shown in FIG. 13, if the fixed magnetization directions (directions indicated by arrows P) of the magnetoresistive elements MR1 and MR2 are opposite to each other, as shown in (a) or (b), If the magnetic fields are opposite to each other with respect to MR1 and MR2, the phases are “in-phase”. If the magnetic fields are the same with respect to the magnetoresistive elements MR1 and MR2, the phases are “opposite”.

DESCRIPTION OF SYMBOLS 10 Magnetic sensor 20 Sensor chip 21 Element formation surface 22 Magnetic block 31 Feedback circuit 32, 32a-32f Magnetic bias circuit A1 First amplifier circuit A2 Second amplifier circuit B Bridge circuit C1 Negative phase coil C2 In phase coil I1 First Feedback current I2 Second feedback current MR1 to MR4 Magnetic resistance elements N0 to N3 Connection point P Fixed magnetization direction R1 to R3 Resistance R31 Fixed resistance R32 Variable resistance R4 Damping resistance S0 to S2 Signal SW Switch Vout Detection voltage Vref Reference potential φ Detection target magnetic field φ1, φ2 Canceling magnetic field

Claims (12)

First and second magnetoresistive elements to which detection target magnetic fields are applied in opposite phases to each other;
A feedback circuit for applying a cancel magnetic field of opposite phase to the first and second magnetoresistive elements based on a difference between resistance values of the first and second magnetoresistive elements;
A magnetic bias circuit for applying a bias magnetic field having the same phase to the first and second magnetoresistive elements based on a sum of resistance values of the first and second magnetoresistive elements. .   The feedback circuit includes a first amplifier circuit that generates a first feedback current based on the difference between the resistance values, and a negative-phase coil that generates the cancel magnetic field based on the first feedback current. The magnetic sensor according to claim 1, wherein:   The magnetic bias circuit includes: a reference resistor; a second amplifier circuit that generates a second feedback current based on a difference between a sum of the resistance values and a resistance value of the reference resistor; 3. The magnetic sensor according to claim 2, further comprising: an in-phase coil that generates the bias magnetic field based on the in-phase coil. A third magnetic resistance element to which the detection target magnetic field is 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 first amplifier circuit detects a difference between a potential at a connection point between the first and second magnetoresistance elements and a potential at a connection point between the third and fourth magnetoresistance 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,
The second amplifier circuit generates the second 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. The magnetic sensor according to claim 3, wherein:   The magnetic sensor according to claim 4, wherein the magnetic bias circuit further includes a switch that applies a reset potential to the one end of the reference resistor.   The magnetic sensor according to claim 3, wherein a resistance value of the reference resistor is variable.   7. The magnetic sensor according to claim 6, wherein the reference resistor includes a magnetic shield element that is magnetically shielded.   The magnetic sensor according to claim 3, wherein the magnetic bias circuit further includes a damping resistor connected in series with the in-phase coil.   9. The magnetic bias circuit according to claim 2, wherein the magnetic bias circuit cancels a disturbance magnetic field applied to the first and second magnetoresistive elements in the same phase by the bias magnetic field. Magnetic sensor.   9. The magnetic bias circuit according to claim 2, wherein the magnetic bias circuit keeps a disturbance magnetic field applied to the first and second magnetic resistance elements in the same phase by the bias magnetic field. 10. A magnetic sensor as described. A sensor chip on which the first and second magnetoresistive elements are formed and which has an element formation surface parallel to a sensitivity axis direction of the first and second magnetoresistive elements;
11. The magnetic head according to claim 2, further comprising: a magnetic block disposed on the element forming surface and located between the first and second magnetic resistance elements. A magnetic sensor according to claim 1.   The magnetic sensor according to claim 11, wherein the negative-phase coil is formed on the sensor chip so as to overlap the first and second magnetoresistive elements.

Images