Magnetic detection device

Abstract

To provide a magnetism detection device capable of increasing a feedback current flowing to a detection coil without reducing resistance of a circuit in which a feedback current flows and without increasing a supply voltage when being equipped with a feedback circuit.SOLUTION: A magnetism detection device 1 includes: a magnet impedance sensor element 2; a main operational amplifier OP_M in which an input terminal is connected to a first end 12a and a second end 12b of a detection coil 12; a first feedback circuit 25 that is connected between an output terminal of the main operational amplifier OP_M and the first end 12a of the detection coil 12 and generates a first feedback voltage VFB1; and a second feedback circuit 26 that is connected between an output terminal of the main operational amplifier OP_M and the second end 12b of the detection coil 12 and generates a second feedback voltage VFB2 obtained by inverting polarity relative to the first feedback voltage VFB1 with a predetermined reference voltage VB as a reference.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a magnetic detection device. [Background technology]

[0002] Patent Document 1 discloses a magnetic detection device that detects the strength of a magnetic field to be detected by using an amorphous magnetic wire as a magnetic sensitive body and a detection coil. The amorphous magnetic wire has a property of generating a magneto-impedance effect (MI effect). That is, when an excitation current is supplied to the amorphous magnetic wire, the amorphous magnetic wire has a property of generating a magnetization change corresponding to the strength of the magnetic field acting on the amorphous magnetic wire. More specifically, the impedance of the amorphous magnetic wire changes as the magnetic permeability in the circumferential direction changes corresponding to the strength of the magnetic field acting on the wire. The detection coil is wound around the amorphous magnetic wire and outputs an induced voltage generated by the magnetization change of the amorphous magnetic wire.

[0003] The excitation current supplied to the amorphous magnetic wire is, for example, a pulse current or a high-frequency current. For example, when a pulse current or a high-frequency current is supplied to the amorphous magnetic wire, a magnetization change corresponding to the strength of the acting magnetic field occurs in the amorphous magnetic wire at the timing of the rise of the current. An induced voltage due to the magnetization change in the amorphous magnetic wire is generated in the detection coil.

[0004] A detection circuit is connected to the detection coil to detect the induced voltage generated in the detection coil. Patent Document 1 discloses a configuration including a detection circuit, an amplifier circuit, and a feedback circuit as the detection circuit. The detection circuit includes a switch that is turned on in response to the timing of the supply of the excitation current, and a hold capacitor for holding the voltage when the switch is turned on. The amplifier circuit is configured with an operational amplifier, and amplifies the voltage held by the hold capacitor. The feedback circuit is configured to connect the output terminal of the amplifier circuit to one end of the detection coil and to magnetically apply negative feedback. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5924503 Summary of the Invention [Problem to be solved by the invention]

[0006] The detection circuit constituting the magnetic detection device disclosed in Patent Document 1 applies magnetic negative feedback by a feedback circuit. Therefore, when the magnetic field to be detected acts on the amorphous magnetic wire, a feedback current flows through the detection coil, and a feedback magnetic field capable of canceling the magnetic field to be detected can be generated. Therefore, if the magnetic field to be detected is canceled by the feedback magnetic field, no magnetic field acts on the amorphous magnetic wire.

[0007] The feedback magnetic field generated by the feedback current flowing through the detection coil depends on the magnitude of the feedback current, so when the magnetic field to be detected is strong, the feedback current needs to be large in order for the detection coil to generate a feedback magnetic field to offset the magnetic field to be detected.

[0008] In the detection circuit disclosed in Patent Document 1, a feedback circuit is connected to one end of a detection coil, and the other end of the detection coil is grounded. Therefore, the magnitude of the feedback current flowing through the detection coil corresponds to the potential difference between the feedback voltage generated by the feedback circuit and the ground voltage.

[0009] One possible way to increase the feedback current in the detection circuit is to reduce the resistance in the circuit through which the feedback current flows. However, reducing the resistance increases the noise in the feedback voltage. The increased noise in the feedback voltage increases the noise in the feedback current, which generates noise in the feedback magnetic field generated in the detection coil. Therefore, in order to generate a desired feedback magnetic field in the detection coil, it is not appropriate to reduce the resistance in the circuit through which the feedback current flows. Another possible way to increase the feedback current is to increase the power supply voltage in the feedback circuit. However, increasing the power supply voltage increases the size of the detection circuit.

[0010] The present invention has been made in consideration of the above background, and aims to provide a magnetic detection device that, when equipped with a feedback circuit, can increase the feedback current flowing in the detection coil without reducing the resistance of the circuit through which the feedback current flows and without increasing the power supply voltage. [Means for solving the problem]

[0011] One aspect of the present invention is a magneto-impedance sensor element including a magneto-sensitive body that generates a magnetization change corresponding to the strength of a magnetic field when an excitation current is supplied, and a detection coil that is wound around the magneto-sensitive body and outputs an induced voltage generated by the magnetization change of the magneto-sensitive body; a main operational amplifier having one of an inverting input terminal and a non-inverting input terminal connected to a first end of the detection coil, and the other of the inverting input terminal and the non-inverting input terminal connected to a second end of the detection coil opposite to the first end; a first feedback circuit connected between an output terminal of the main operational amplifier and the first end of the detection coil, for generating a first feedback voltage for generating a feedback current in the detection coil; a second feedback circuit connected between the output terminal of the main operational amplifier and the second end of the detection coil, the second feedback circuit generating a second feedback voltage having a polarity inverted with respect to the first feedback voltage when a predetermined reference voltage is used as a reference, in order to generate the feedback current in the detection coil; The magnetic detection device includes: Effect of the Invention

[0012] The magnetic detection device in the above embodiment includes a main operational amplifier connected to the detection coil, and a feedback circuit connecting the output terminal of the main operational amplifier and the detection coil. With this configuration, when the magnetic field to be detected acts on the magnetic sensitive body, a feedback current is generated in the detection coil, and the detection coil generates a feedback magnetic field to offset the magnetic field to be detected. If the feedback magnetic field is in a state where it completely offsets the magnetic field to be detected, the feedback current will be in a state corresponding to the strength of the magnetic field to be detected. In other words, if the feedback magnetic field can completely offset the magnetic field to be detected, the magnetic field to be detected can be detected with high accuracy by detecting the feedback current or a physical quantity corresponding to the feedback current.

[0013] When the feedback magnetic field cancels out the magnetic field to be detected, the magnetic field is not acting on the magnetosensitive body. Therefore, the feedback current corresponding to the magnetic field to be detected does not depend on the electromagnetic characteristics of the magnetosensitive body. The relationship between the magnetic field to be detected and the feedback current is linear. Therefore, by detecting the feedback current or a physical quantity corresponding to the feedback current, the detection accuracy of the magnetic field to be detected can be improved.

[0014] Furthermore, according to the magnetic detection device in the above aspect, both ends of the detection coil of the magneto-impedance sensor element are connected to the inverting input terminal and the non-inverting input terminal of the main operational amplifier. Furthermore, the magnetic detection device includes two feedback circuits. One of the two feedback circuits is a first feedback circuit connected between the output terminal of the main operational amplifier and a first end of the detection coil. The other of the two feedback circuits is a second feedback circuit connected between the output terminal of the main operational amplifier and a second end of the detection coil.

[0015] With this configuration, the feedback current generated in the detection coil is a current corresponding to the potential difference between the first feedback voltage generated by the first feedback circuit and the second feedback voltage generated by the second feedback circuit. In other words, the physical quantity corresponding to the feedback current described above can be, for example, the potential difference between the first feedback voltage and the second feedback voltage.

[0016] The second feedback voltage is a voltage whose polarity is inverted with respect to the first feedback voltage when a predetermined reference voltage is used as a reference. Therefore, the potential difference between the first feedback voltage and the second feedback voltage can be increased. In other words, the feedback current can be increased. In order to increase the feedback current, the resistance of the circuit through which the feedback current flows is not reduced, and the power supply voltage is not increased.

[0017] As described above, according to the above aspect, when a feedback circuit is provided, a magnetic detection device can be provided that can increase the feedback current flowing in the detection coil without reducing the resistance of the circuit through which the feedback current flows and without increasing the power supply voltage. [Brief description of the drawings]

[0018] [Figure 1] 1 is a diagram showing a configuration of a magnetic detection device according to a first embodiment. [Diagram 2] 5A to 5C are diagrams illustrating the operation of the magneto-impedance sensor element constituting the magnetic detection device of the first embodiment. [Diagram 3] 5A to 5C are diagrams illustrating the operation of the magnetic detection device according to the first embodiment. [Figure 4] FIG. 2 is a diagram showing a configuration of a magnetic detection device of a comparative example. [Diagram 5] 5A to 5C are diagrams illustrating the operation of a magnetic detection device of a comparative example. [Figure 6] FIG. 4 is a diagram for explaining the range of magnetic fields to be detected in the first embodiment and a comparative example. [Figure 7] FIG. 11 is a diagram showing the configuration of a magnetic detection device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The magnetic detection device can be used in various applications for the purpose of detecting the strength of a magnetic field, for example, in an electronic compass, a foreign object detection sensor, a magnetic positioning system, etc.

[0020] In the magnetic detection device, the magnetic sensitive body constituting the magneto-impedance sensor element can be a magnetic wire, particularly an amorphous magnetic wire. Note that the magnetic sensitive body can be made of a material other than an amorphous magnetic wire as long as it has the property of causing a magnetization change corresponding to the strength of a magnetic field when an excitation current is supplied. In addition, the excitation current supplied to the magnetic sensitive body can be, for example, a periodic current such as a pulse current or a high-frequency current.

[0021] Moreover, in the magnetic detection device, the first feedback circuit can be configured to include a first feedback operational amplifier having an input terminal connected to the output terminal side of the main operational amplifier and an output terminal connected to the first end side of the detection coil, and the second feedback circuit can be configured to include a second feedback operational amplifier having an input terminal connected to the output terminal side of the main operational amplifier and an output terminal connected to the second end side of the detection coil.

[0022] In this case, the first feedback voltage is the voltage at the output terminal of the first feedback operational amplifier, and the second feedback voltage is the voltage at the output terminal of the second feedback operational amplifier, and at the input terminal of the first feedback operational amplifier connected to the output terminal side of the main operational amplifier and the input terminal of the second feedback operational amplifier connected to the output terminal side of the main operational amplifier, one input terminal is an inverting input terminal and the other input terminal is a non-inverting input terminal.

[0023] With this configuration, the first feedback voltage and the second feedback voltage can be inverted with respect to a predetermined reference voltage, so that the potential difference between the first feedback voltage and the second feedback voltage can be increased, and the feedback current can be increased.

[0024] In addition, by setting the amplification factor of the first feedback circuit and the amplification factor of the second feedback circuit to be the same, the second feedback voltage can be an inverted voltage of the first feedback voltage when the predetermined reference voltage is used as a reference. Note that the amplification factor of the first feedback circuit and the amplification factor of the second feedback circuit can be set to different values.

[0025] In the magnetic detection device, the first feedback circuit may be configured to include the first feedback operational amplifier and a first impedance circuit connected between an output terminal of the first feedback operational amplifier and the first end of the detection coil to suppress the induced voltage output by the detection coil from moving toward the first feedback operational amplifier. Furthermore, the second feedback circuit may be configured to include the second feedback operational amplifier and a second impedance circuit connected between an output terminal of the second feedback operational amplifier and the second end of the detection coil to suppress the induced voltage output by the detection coil from moving toward the second feedback operational amplifier.

[0026] With the above configuration, when the magnetization of the magnetic sensitive body changes and the induced voltage is generated in the detection coil, the induced voltage can be prevented from moving to the first feedback operational amplifier and can also be prevented from moving to the second feedback operational amplifier. As a result, the feedback current can be made to have a magnitude that can generate a feedback magnetic field to offset the magnetic field to be detected.

[0027] The impedance of the first impedance circuit and the impedance of the second impedance circuit can be set to be the same. By configuring in this way, the first feedback voltage and the second feedback voltage can be set to desired inverted voltages. The impedance of the first impedance circuit and the impedance of the second impedance circuit can be set to different values.

[0028] Furthermore, the magnetic detection device may also include a common feedback input voltage generation circuit connected to the output terminal of the main operational amplifier, performing at least one of phase adjustment processing, differentiation processing, and integration processing on the output voltage of the main operational amplifier, and generating a common feedback input voltage for the first feedback circuit and the second feedback circuit.

[0029] When generating a voltage that has undergone the above-mentioned processing as an input voltage for the first feedback circuit and the second feedback circuit, the circuit configuration can be simplified by providing one common feedback input voltage generating circuit compared to providing separate feedback input voltage generating circuits.

[0030] The magnetic detection device may further include a first input circuit connected between the first end of the detection coil and the inverting input terminal of the main operational amplifier, for holding a voltage at the first end at a predetermined timing and inputting the held voltage at the first end to the inverting input terminal of the main operational amplifier, and a second input circuit connected between the second end of the detection coil and the non-inverting input terminal of the main operational amplifier, for holding a voltage at the second end at a timing identical to the predetermined timing and inputting the held voltage at the second end to the non-inverting input terminal of the main operational amplifier. In this manner, by providing the first input circuit and the second input circuit, the first feedback voltage and the second feedback voltage can be made to be desired inverted voltages.

[0031] Moreover, the predetermined reference voltage can be a positive voltage. That is, the first feedback voltage and the second feedback voltage can be inverted voltages with respect to the predetermined reference voltage, which is a positive voltage. This allows the detection circuit to be configured to operate in the range of positive voltages. In this case, a single-power supply operational amplifier can be applied as the main operational amplifier. The predetermined reference voltage can also be a ground voltage. In this case, it is preferable that the detection circuit be operable at positive and negative voltages.

[0032] Furthermore, the magnetic detection device may include a common reference power supply that applies the positive voltage as the predetermined reference voltage to the first feedback circuit and the second feedback circuit, and the reference power supply for the first feedback circuit and the reference power supply for the second feedback circuit may be smaller in circuit size than when separate power supplies are used.

[0033] The magnetic detection device may further include a signal output unit that outputs the potential difference between the first feedback voltage and the second feedback voltage, or the feedback current, as a detection signal representing the strength of the magnetic field to be detected acting on the magnetic sensitive body. As described above, the feedback current has a magnitude corresponding to the strength of the magnetic field to be detected. Therefore, the magnetic field to be detected can be reliably detected by outputting the feedback current as a detection signal. Furthermore, the potential difference between the first feedback voltage and the second feedback voltage is a physical quantity corresponding to the feedback current. Therefore, the signal output unit constituting the magnetic detection device may also output the potential difference between the first feedback voltage and the second feedback voltage as a detection signal.

[0034] (Embodiment 1) 1. Configuration of magnetic detection device 1 A magnetic detection device 1 in the first embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the magnetic detection device 1 of this embodiment includes a magneto-impedance sensor element 2 (hereinafter, referred to as an "MI sensor element") and a detection circuit 3.

[0035] The MI sensor element 2 is subjected to a magnetic field B ACT The MI sensor element 2 includes a magnetosensitive body 11 and a detection coil 12. The magnetosensitive body 11 detects a magnetic field B acting on the magnetosensitive body 11 when an excitation current is supplied thereto. ACT In detail, when a pulse current or a high-frequency current is supplied as an excitation current, the magnetosensitive element 11 is magnetized by the magnetic field B ACT The impedance changes as the magnetic permeability in the circumferential direction changes in response to the strength of the magnetic field B. ACTWhen an excitation current is supplied to the magnetosensitive body 11 in a state where the magnetic field B is acting on the magnetosensitive body 11, the magnetization of the magnetosensitive body 11 changes. The magnetosensitive body 11 is made of, for example, a magnetic wire, particularly an amorphous magnetic wire. In the following, the magnetic field B acting on the magnetosensitive body 11 is ACT is also referred to as the "acting magnetic field" as appropriate.

[0036] Here, the magnetic field B acting on the magnetosensitive body 11 is ACT is the magnetic field to be detected, which is the external magnetic field acting on the magnetosensitive body 11. IN , and the feedback magnetic field B FB Therefore, the return magnetic field B FB is the magnetic field to be detected B IN In the case where the magnetic field B is completely cancelled out, the magnetic field is not acting on the magnetic sensitive body 11. IN Even if the feedback magnetic field B FB By generating the magnetic field B ACT is almost zero.

[0037] The detection coil 12 is wound around the magnetosensitive body 11. A magnetic field B ACT When an exciting current is supplied, an induced voltage is generated in the detection coil 12 due to a change in magnetization of the magnetosensitive member 11. Therefore, the detection coil 12 outputs the induced voltage generated by the change in magnetization of the magnetosensitive member 11.

[0038] The detection circuit 3 is electrically connected to the MI sensor element 2 and detects the magnetic field B IN The detection circuit 3 includes an excitation circuit 21, a main amplifier circuit 22, a first input circuit 23, a second input circuit 24, a first feedback circuit 25, a second feedback circuit 26, a signal output section 27, and a reference power supply 28.

[0039] The excitation circuit 21 supplies the magnetosensitive element 11 with an excitation current I IN The excitation circuit 21 supplies a pulse current or a high-frequency current as the excitation current. Furthermore, the excitation circuit 21 outputs a switch timing signal Sg for holding the induced voltage in the detection coil 12.

[0040] The main amplifier circuit 22 amplifies the potential difference between the first end 12a and the second end 12b of the detection coil 12. The second end 12b of the detection coil 12 is the end opposite to the first end 12a. The main amplifier circuit 22 includes a main operational amplifier OP_M. In this embodiment, the main amplifier circuit 22 includes resistors R1, R2, etc. for defining an amplification factor. However, the main amplifier circuit 22 can be of various amplifier types as long as it is configured to amplify a signal at a predetermined amplification factor.

[0041] One of the inverting input terminal and the non-inverting input terminal of the main operational amplifier OP_M is connected to the first end 12a of the detection coil 12, and the other of the inverting input terminal and the non-inverting input terminal is connected to the second end 12b of the detection coil 12. In this embodiment, the inverting input terminal of the main operational amplifier OP_M is connected to the first end 12a of the detection coil 12, and the non-inverting input terminal is connected to the second end 12b of the detection coil 12. The main operational amplifier OP_M is also configured as a single-power supply operational amplifier. A reference power supply 28 is connected to the positive power supply terminal of the main operational amplifier OP_M, and a maximum voltage Vcc_A of the reference power supply 28 is applied thereto. The negative power supply terminal of the main operational amplifier OP_M is grounded.

[0042] The first input circuit 23 is connected between the first end 12a of the detection coil 12 and one of the inverting input terminal and the non-inverting input terminal of the main operational amplifier OP_M. The first input circuit 23 holds the voltage of the first end 12a at a predetermined timing, and inputs the held voltage of the first end 12a to one of the inverting input terminal and the non-inverting input terminal of the main operational amplifier OP_M. In this embodiment, the first input circuit 23 is connected between the first end 12a of the detection coil 12 and the inverting input terminal of the main operational amplifier OP_M.

[0043] The first input circuit 23 includes a capacitor C1 and a resistor R3 that form a high-pass filter, a switch Sw1 that turns on at a predetermined timing, and a hold capacitor C2. The high-pass filter outputs a voltage with a frequency higher than the cutoff frequency at the first end 12a of the detection coil 12. The resistor R3 that forms the high-pass filter can be replaced with a component having a predetermined impedance, such as an inductor. The switch Sw1 turns on when the switch timing signal Sg is output by the excitation circuit 21 described above.

[0044] The hold capacitor C2 holds the voltage when the switch Sw1 is turned on. One end of the hold capacitor C2 is connected to the switch Sw1, and the other end of the hold capacitor C2 is connected to a predetermined reference potential Vcc_B.

[0045] The second input circuit 24 is connected between the second end 12b of the detection coil 12 and the other of the inverting input terminal and the non-inverting input terminal of the main operational amplifier OP_M. The second input circuit 24 holds the voltage of the second end 12b at a predetermined timing, and inputs the held voltage of the second end 12b to the other of the inverting input terminal and the non-inverting input terminal of the main operational amplifier OP_M. In this embodiment, the second input circuit 24 is connected between the second end 12b of the detection coil 12 and the non-inverting input terminal of the main operational amplifier OP_M. The predetermined timing at which the second input circuit 24 holds is the same as the predetermined timing at which the first input circuit 23 holds.

[0046] The second input circuit 24 is disposed symmetrically with the first input circuit 23, and constitutes a circuit similar to the first input circuit 23. The second input circuit 24 includes a capacitor C3 and a resistor R4 constituting a high-pass filter, a switch Sw2 that turns on at a predetermined timing, and a hold capacitor C4. The high-pass filter outputs a voltage having a frequency higher than the cutoff frequency at the second end 12b of the detection coil 12. The resistor R4 constituting the high-pass filter can be replaced with a component having a predetermined impedance, such as an inductor. The switch Sw2 turns on at the timing when the switch timing signal Sg is output by the excitation circuit 21 described above.

[0047] The hold capacitor C4 holds the voltage when the switch Sw2 is turned on. One end of the hold capacitor C4 is connected to the switch Sw2, and the other end of the hold capacitor C4 is connected to a predetermined reference potential Vcc_B.

[0048] The first feedback circuit 25 is connected between the output terminal of the main operational amplifier OP_M and the first end 12a of the detection coil 12. The first feedback circuit 25 supplies a feedback current I FB The first feedback voltage V FB1 Generate.

[0049] The first feedback circuit 25 includes a circuit 25a including a first feedback operational amplifier OP_FB1 and a first impedance circuit 25b. The circuit 25a including the first feedback operational amplifier OP_FB1 may be an amplifier circuit or a buffer circuit. In this embodiment, the circuit 25a is an inverting amplifier circuit.

[0050] The first feedback operational amplifier OP_FB1 is configured as a single power supply operational amplifier. A reference power supply 28 is connected to a positive power supply terminal of the first feedback operational amplifier OP_FB1, and a maximum voltage Vcc_A of the reference power supply 28 is applied to the positive power supply terminal of the first feedback operational amplifier OP_FB1. A negative power supply terminal of the first feedback operational amplifier OP_FB1 is grounded.

[0051] An input terminal of the first feedback operational amplifier OP_FB1 is connected to the output terminal side of the main operational amplifier OP_M. In this embodiment, an inverting input terminal of the first feedback operational amplifier OP_FB1 is connected to the output terminal side of the main operational amplifier OP_M via a resistor R5. The first feedback operational amplifier OP_FB1 operates so that the voltage of the inverting input terminal matches the voltage of the non-inverting input terminal.

[0052] The non-inverting input terminal of the first feedback operational amplifier OP_FB1 is connected to the reference power supply 28 via a resistor R7. For example, a voltage "Vcc_A / 2" that is half the maximum voltage Vcc_A of the reference power supply 28 is applied to the end of the resistor R7 opposite to the first feedback operational amplifier OP_FB1. The voltage "Vcc_A / 2" is the predetermined reference voltage VB. In this embodiment, the predetermined reference voltage VB is set to a positive voltage.

[0053] The output terminal of the first feedback operational amplifier OP_FB1 is connected to the first end 12a of the detection coil 12. The first feedback voltage V FB1 is the voltage at the output terminal of the first feedback operational amplifier OP_FB1. In addition, since the circuit 25a constituting the first feedback operational amplifier OP_FB1 is an inverting amplifier circuit, the amplification factor is determined by the ratio of resistors R5 and R6.

[0054] The first impedance circuit 25b is connected between the output terminal of the first feedback operational amplifier OP_FB1 and the first end 12a of the detection coil 12. The first impedance circuit 25b is configured to suppress the induced voltage output by the detection coil 12 from moving toward the first feedback operational amplifier OP_FB1. In this embodiment, the first impedance circuit 25b is configured by a resistor R8 and an inductor L1. However, various impedance circuits can be applied to the first impedance circuit 25b.

[0055] The second feedback circuit 26 is connected between the output terminal of the main operational amplifier OP_M and the second end 12b of the detection coil 12. The second feedback circuit 26 supplies a feedback current I FB The second feedback voltage V FB2Generate.

[0056] The second feedback circuit 26 includes a circuit 26a configured by a second feedback operational amplifier OP_FB2, and a second impedance circuit 26b. The circuit 26a configured by the second feedback operational amplifier OP_FB2 may be an amplifier circuit or a buffer circuit. However, the circuit 26a configures a circuit that is inverted from the circuit 25a that configures the first feedback circuit 25. In this embodiment, the circuit 26a is exemplified as a non-inverting amplifier circuit.

[0057] The second feedback operational amplifier OP_FB2 is configured by a single power supply operational amplifier. A reference power supply 28 is connected to a positive power supply terminal of the second feedback operational amplifier OP_FB2, and a maximum voltage Vcc_A of the reference power supply 28 is applied to the positive power supply terminal of the second feedback operational amplifier OP_FB2. A negative power supply terminal of the second feedback operational amplifier OP_FB2 is grounded.

[0058] The input terminal of the second feedback operational amplifier OP_FB2 is connected to the output terminal side of the main operational amplifier OP_M. In this embodiment, the inverting input terminal of the second feedback operational amplifier OP_FB2 is connected to the reference power supply 28 via a resistor R9. A voltage "Vcc_A / 2" that is half the maximum voltage Vcc_A of the reference power supply 28 is applied to the end of the resistor R9 opposite to the second feedback operational amplifier OP_FB2. The voltage "Vcc_A / 2" is the predetermined reference voltage VB. The resistor R9 is the same resistor as the resistor R7 in the first feedback circuit 25. The second feedback operational amplifier OP_FB2 operates so that the voltage of the inverting input terminal coincides with the voltage of the non-inverting input terminal.

[0059] The non-inverting input terminal of the second feedback operational amplifier OP_FB2 is connected to the output terminal side of the main operational amplifier OP_M via a resistor R11. In this embodiment, the resistor R11 is the same resistor as the resistor R5 in the first feedback circuit 25.

[0060] The output terminal of the second feedback operational amplifier OP_FB2 is connected to the second end 12b of the detection coil 12. The second feedback voltage V FB2is the voltage at the output terminal of the second feedback operational amplifier OP_FB2. In addition, since the circuit 26a constituting the second feedback operational amplifier OP_FB2 is a non-inverting amplifier circuit, the amplification factor is determined by the ratio of resistors R9 and R10.

[0061] As described above, the first feedback circuit 25 and the second feedback circuit 26 are configured to generate the second feedback voltage V FB2 is the first feedback voltage V FB1 The polarity of the voltage VB is inverted with respect to the voltage VB. Here, the polarity refers to whether the polarity is positive or negative when the predetermined reference voltage VB is set to zero.

[0062] In this embodiment, the amplification factor of the circuit 26a constituting the non-inverting amplifier circuit in the second feedback circuit 26 is set to be the same as the amplification factor of the circuit 25a constituting the inverting amplifier circuit in the first feedback circuit 25. Therefore, the second feedback voltage V FB2 is the first feedback voltage V FB1 can be an inverted voltage with respect to a predetermined reference voltage VB. In this case, the first feedback voltage V FB1 The absolute value of the difference between the second feedback voltage V and the predetermined reference voltage VB. FB2 and the absolute value of the difference between the predetermined reference voltage VB is 1.

[0063] However, the amplification factor of the circuit 25a and the amplification factor of the circuit 26a can be set to different values. In this case, the first feedback voltage V FB1 The absolute value of the difference between the second feedback voltage V and the predetermined reference voltage VB. FB2 and the absolute value of the difference between the predetermined reference voltage VB is a value other than 1.

[0064] The second impedance circuit 26b is connected between the output terminal of the second feedback operational amplifier OP_FB2 and the second end 12b of the detection coil 12. The second impedance circuit 26b is configured to suppress the induced voltage output by the detection coil 12 from moving toward the second feedback operational amplifier OP_FB2. In this embodiment, the second impedance circuit 26b is configured by a resistor R12 and an inductor L2. However, various impedance circuits can be applied to the second impedance circuit 26b. The impedance of the second impedance circuit 26b is set to be the same as the impedance of the first impedance circuit 25b.

[0065] The signal output unit 27 outputs a first feedback voltage V FB1 and the second feedback voltage V FB2 The potential difference ΔVx with the feedback current I FB The magnetic field B to be detected acting on the magnetosensitive body 11 IN The signal is output as a detection signal representing the strength of the light.

[0066] In this embodiment, the first feedback voltage V FB1 and the potential difference between the reference voltage VB and the second feedback voltage V FB2 The potential difference between the first feedback voltage V FB1 and the second feedback voltage V FB2 It is half the potential difference ΔVx with the first feedback voltage V FB1 and the potential difference between the reference voltage VB and the second feedback voltage V FB2 The potential difference between the reference voltage V and the magnetic field B IN Therefore, the signal output unit 27 corresponds to the first feedback voltage V FB1 and a predetermined reference voltage VB, or the second feedback voltage V FB2 and a predetermined reference voltage VB, the magnetic field B IN It is also possible to output the signal as a detection signal representing the strength of the light.

[0067] The reference power supply 28 applies a power supply voltage to the positive power supply terminals of the main operational amplifier OP_M, the first feedback operational amplifier OP_FB1, and the second feedback operational amplifier OP_FB2. Furthermore, the reference power supply 28 also functions as a common power supply that applies a positive voltage as a predetermined reference voltage VB to the first feedback operational amplifier OP_FB1 and the second feedback operational amplifier OP_FB2.

[0068] 2. Operation of MI sensor element 2 Next, the operation of the MI sensor element 2 will be described with reference to Fig. 2. Here, it is assumed that the MI sensor element 2 is not connected to the detection circuit 3 shown in Fig. 1. That is, the operation of the MI sensor element 2 alone will be described.

[0069] FIG. 2(a) shows the excitation current I IN is a pulse current. The MI sensor element 2 can be designed to vary the response speed of the induced voltage with respect to changes in the rising edge of the pulse current. FIG. 2(b) shows the induced voltage Vs1 when the MI sensor element 2 has a high response when a magnetic field is applied to the MI sensor element 2. FIG. 2(c) shows the induced voltage Vs2 when the MI sensor element 2 has a low response when a magnetic field is applied to the MI sensor element 2.

[0070] As shown in Fig. 2(a), the excitation current I IN is supplied to the magnetosensitive body 11, the magnetization of the magnetosensitive body 11 changes according to the strength of the magnetic field acting on the magnetosensitive body 11 due to the change in the rising edge of the pulse current. The change in magnetization of the magnetosensitive body 11 generates an induced voltage in the detection coil 12, as shown in FIG. 2(b) or FIG. 2(c).

[0071] 2(b), when the MI sensor element 2 is highly responsive, the induced voltage Vs1 exhibits damped oscillation immediately after the rise of the pulse current. Then, at time T, the induced voltage Vs1 reaches a peak value. The peak value of the induced voltage Vs1 corresponds to the strength of the magnetic field acting on the MI sensor element 2. Note that when the MI sensor element 2 is highly responsive, the induced voltage Vs1 exhibits damped oscillation even immediately after the fall of the pulse current.

[0072] 2(c), when the MI sensor element 2 has a low response, the induced voltage Vs2 rises gradually immediately after the pulse current rises. Then, at time T, the induced voltage Vs2 reaches a peak value. The peak value of the induced voltage Vs2 corresponds to the strength of the magnetic field acting on the MI sensor element 2. Then, the induced voltage Vs2 falls gradually immediately after the pulse current falls.

[0073] In the magnetic detection device 1 of this embodiment, the MI sensor element 2 can be configured to have a high response or a low response.

[0074] 3. Operation of the magnetic detection device 1 Next, the operation of the magnetic detection device 1 will be described with reference to FIG. IN When the voltage V1 to V5 at each point in the detection circuit 3 and the first feedback voltage V FB1 , the second feedback voltage V FB2 , feedback current I FB , the return magnetic field B FB , working magnetic field B ACT The behavior of will be explained.

[0075] As shown in FIG. 3(a), a magnetic field B IN In the example, the direction of the magnetic field changes periodically, and the strength of the magnetic field changes like a sine wave. IN The behaviors shown are examples for the purpose of making the explanation easier to understand, and in reality, any behavior may be used.

[0076] If the detection circuit 3 does not include the first feedback circuit 25 and the second feedback circuit 26, as described with reference to FIG. 2, the potential difference between both ends of the detection coil 12 is the magnetic field B IN However, in this embodiment, the detection circuit 3 includes the first feedback circuit 25 and the second feedback circuit 26 as described above. Therefore, the feedback current I FB is generated.

[0077] In this embodiment, as shown in FIG. 3(h), the feedback current I FB is generated, and the feedback current I FB When the magnetic field flows through the detection coil 12, as shown in FIG. 3(i), the detection coil 12 is induced by a feedback magnetic field B FB The feedback magnetic field B FB is the magnetic field to be detected B IN If it were possible to completely cancel out the magnetic field B acting on the magneto-sensitive body 11, as shown in FIG. ACT becomes zero.

[0078] In other words, the magnetic field B to be detected is applied to the magnetosensitive body 11. IN Even if the magnetic field B acting on the magnetosensitive body 11 is ACT Therefore, the magnetosensitive element 11 is driven by the excitation current I IN Even if the applied magnetic field B ACT is approximately zero, the induced voltage in the detection coil 12 is approximately zero. As shown in Figures 3(b) and 3(c), the voltages V1 and V2 across the detection coil 12 are approximately zero.

[0079] Since the voltages V1 and V2 across the detection coil 12 are almost zero, the voltages V3 and V4 at the inverting and non-inverting input terminals of the main amplifier circuit 22 are also almost zero, as shown in Figures 3(d) and 3(e). Therefore, the voltage V5 at the output terminal of the main amplifier circuit 22 is also almost zero, as shown in Figure 3(f).

[0080] As described above, the detection circuit 3 includes the first feedback circuit 25 and the second feedback circuit 26, so that the feedback current IFB is generated. The feedback current I FB is the first feedback voltage V FB1 and the second feedback voltage V FB2 It is determined by the potential difference ΔVx between the first impedance circuit 25b and the second impedance circuit 26b, and the impedance in the circuit through the detection coil 12. In this embodiment, the impedance in the circuit through the detection coil 12 is a combination of the impedance of the first impedance circuit 25b and the impedance of the second impedance circuit 26b.

[0081] And the second feedback voltage V FB2 is the first feedback voltage V FB1 In this embodiment, the second feedback voltage V FB2 is the first feedback voltage V FB1 is inverted with respect to a predetermined reference voltage VB.

[0082] Therefore, the first feedback voltage V FB1 and the second feedback voltage V FB2 The first feedback voltage V FB1 and the second feedback voltage V FB2 The potential difference ΔVx is the first feedback voltage V FB1 The first feedback voltage V FB1 and the second feedback voltage V FB2 The potential difference ΔVx is the first feedback voltage V FB1 The second feedback voltage V FB2 The potential difference between the input voltage Vp and the predetermined reference voltage VB is doubled.

[0083] Thus, the first feedback voltage V FB1 and the second feedback voltage V FB2 By increasing the potential difference ΔVx with FB It is possible to generate a large feedback current I FB This means that the return magnetic field B FB In other words, it is possible to increase the magnetic field B INThe feedback magnetic field B to cancel FB Therefore, a large magnetic field B IN It becomes possible to detect.

[0084] 4. Magnetic detection device 100 of comparative example The configuration of a magnetic detection device 100 of the comparative example will be described with reference to Fig. 4. The magnetic detection device 100 includes an MI sensor element 2 and a detection circuit 103. The MI sensor element 2 is the same as the MI sensor element 2 in the first embodiment described above.

[0085] The detection circuit 103 includes an excitation circuit 121, a main amplifier circuit 122, an input circuit 123, and a feedback circuit 124. In the components of the detection circuit 103, the same components as those in the first embodiment are denoted by the same reference numerals.

[0086] The excitation circuit 121 supplies the magnetosensitive element 11 with an excitation current I IN and outputs a switch timing signal Sg for holding the induced voltage of the detection coil 12 to the switch Sw1 of the input circuit 123. The main amplifier circuit 122 is configured with a main operational amplifier OP_M. In the comparative example, the main operational amplifier OP_M is configured with a dual power supply operational amplifier. The input circuit 123 has a configuration similar to that of the first input circuit 23 of the first embodiment. The feedback circuit 124 has a configuration substantially similar to that of the first feedback circuit 25 of the first embodiment. The feedback circuit 124 includes a circuit 124a configured with a feedback operational amplifier OP_FB, and an impedance circuit 124b. The feedback operational amplifier OP_FB is configured with a dual power supply operational amplifier.

[0087] The operation of the magnetic detection device 100 of the comparative example will be described with reference to Fig. 5. As shown in Fig. 5(a), a magnetic field B to be detected acting on the magnetic sensitive body 11 is IN As an example, consider the case where the magnetic field direction changes periodically, and further, the case where the magnetic field strength changes like a sine wave.

[0088] In this case, since the detection circuit 103 includes the feedback circuit 124, the voltages V11 and V12 across the detection coil 12 are almost zero, as shown in Figures 5(b) and 5(c). Since the voltages V11 and V12 across the detection coil 12 are almost zero, the voltage V13 at the input terminal of the main amplifier circuit 122 is also almost zero, as shown in Figure 5(d). Therefore, the voltage V14 at the output terminal of the main amplifier circuit 122 is also almost zero, as shown in Figure 5(e).

[0089] In addition, the detection circuit 103 includes a feedback circuit 124, so that the feedback current I FB is generated. The feedback current I FB is the feedback voltage V FB and the ground voltage which is a predetermined reference voltage, and the impedance in the circuit through the detection coil 12. In the comparative example, the impedance in the circuit through the detection coil 12 is the impedance of the impedance circuit 124b.

[0090] Therefore, the feedback voltage V FB The feedback voltage V FB The feedback current I according to the potential difference ΔVy between the FB is generated in the detection coil 12, and the feedback magnetic field B FB The magnetic field to be detected B IN is the feedback magnetic field B FB When the magnetic field B acting on the magneto-sensitive body 11 is canceled out by the magnetic field B ACT is almost zero.

[0091] 5. Comparison between the first embodiment and the comparative example The magnetic detection device 1 of the first embodiment and the magnetic detection device 100 of the comparative example will be compared with reference to Fig. 6. In Fig. 6, the magnetic field B IN and the first feedback voltage V FB1 and the second feedback voltage V FB2 The relationship between the potential difference ΔVx and the first feedback voltage V FB1 and the second feedback voltage V FB2 The potential difference ΔVx between the feedback current I FBTherefore, in the first embodiment, the magnetic field to be detected B IN and the feedback current I FB The relationship between is similar.

[0092] In addition, in FIG. 6, the magnetic field B IN and the feedback voltage V FB In the comparative example, the second end 12b of the detection coil 12 is grounded, so the feedback voltage V FB The potential difference ΔVy between the feedback current I FB Therefore, in the comparative example, the magnetic field to be detected B IN and the feedback current I FB The relationship between the feedback voltage V FB The potential difference ΔVy between the feedback voltage V FB Matches.

[0093] In the first embodiment, the magnetic field to be detected B IN In the range of ΔBx centered on zero, the detected magnetic field B IN The relationship between the potential difference ΔVx and the magnetic field B to be detected is linear. IN The larger the potential difference ΔVx, the larger the increase rate is constant.

[0094] However, the magnetic field to be detected B IN When the strength of the magnetic field in one direction becomes larger than Bx_max, the potential difference ΔVx reaches the upper positive limit, and a larger feedback current I FB Therefore, the magnetic field to be detected B IN Even if the strength of the magnetic field in one direction becomes greater than Bx_max, the potential difference ΔVx remains at the positive upper limit. FB1 reaches its upper limit, the potential difference ΔVx reaches its upper positive limit.

[0095] Similarly, the magnetic field to be detected B INWhen the strength of the magnetic field in the other direction becomes greater than the absolute value of Bx_min, the potential difference ΔVx reaches the negative lower limit, and a larger feedback current I FB Therefore, the magnetic field to be detected B IN Even if the strength of the magnetic field in the other direction becomes greater than the absolute value of Bx_min, the potential difference ΔVx remains at the negative lower limit value. FB2 reaches the upper limit, the potential difference ΔVx reaches the negative lower limit.

[0096] On the other hand, in the comparative example, the magnetic field to be detected B IN In the range of ΔBy centered on zero, the magnetic field B IN The relationship between the potential difference ΔVy and the magnetic field B to be detected is linear. IN The larger the potential difference ΔVy, the larger the increase rate is constant.

[0097] However, the magnetic field to be detected B IN When the strength of the magnetic field in one direction becomes larger than By_max, the potential difference ΔVy reaches the upper positive limit, and a larger feedback current I FB Therefore, the magnetic field to be detected B IN Even if the strength of the magnetic field in one direction becomes greater than By_max, the potential difference ΔVy remains at the positive upper limit. FB reaches its upper positive limit, the potential difference ΔVy reaches its upper positive limit.

[0098] Similarly, the magnetic field to be detected B IN When the strength of the magnetic field in the other direction becomes larger than the absolute value of By_min, the potential difference ΔVy reaches the negative lower limit, and a larger feedback current I FB Therefore, the magnetic field to be detected B IN Even if the strength of the magnetic field in the other direction becomes greater than the absolute value of By_min, the potential difference ΔVy remains at the negative lower limit. FB reaches the negative lower limit, the potential difference ΔVy reaches the negative lower limit.

[0099] That is, in both the magnetic detection device 1 of the first embodiment and the magnetic detection device 100 of the comparative example, the magnetic field to be detected B IN The detectable range ΔBx, ΔBy is the feedback current I FB It depends on the maximum value of

[0100] In the magnetic detection device 1 of the first embodiment, the feedback current I FB The maximum value of the first feedback voltage V FB1 and the second feedback voltage V FB2 It depends on the magnitude of the potential difference ΔVx (shown in FIG. 3(g)) between the second feedback voltage V FB2 is the first feedback voltage V FB1 In particular, the second feedback voltage V FB2 is the first feedback voltage V FB1 Therefore, the first feedback voltage V FB1 and the second feedback voltage V FB2 The first feedback voltage V FB1 and the second feedback voltage V FB2 The potential difference ΔVx is the first feedback voltage V FB1 The potential difference between the input voltage Vp and the predetermined reference voltage VB is doubled.

[0101] On the other hand, in the magnetic detection device 100 of the comparative example, the feedback current I FB The maximum value of is the feedback voltage V FB The magnitude of the potential difference ΔVy (shown in FIG. 5(f)) between the Vcc and ground voltage depends on the magnitude of the potential difference ΔVy (shown in FIG. 5(f)).

[0102] The first feedback voltage V in the first embodiment FB1 and the second feedback voltage V FB2 The maximum value of the feedback voltage V FB The maximum value of depends on the maximum voltage that the power supply can apply. Also, the feedback current I FB depends on the impedance in the circuit through the detection coil 12.

[0103] Therefore, in the first embodiment and the comparative example, when the maximum voltage that the power supply can apply is the same and the impedance of the circuit flowing through the detection coil 12 is the same, the feedback current I FB The maximum value of the feedback current I FB In other words, the magnetic detection device 1 of the first embodiment has a larger magnetic field to be detected than the magnetic detection device 100 of the comparative example even if the power supply voltage and impedance are the same. IN It can double the detectable range of

[0104] 6. Effects of the First Embodiment The magnetic detection device 1 of this embodiment includes a main operational amplifier OP_M connected to the detection coil 12, and feedback circuits 25 and 26 connecting the output terminal of the main operational amplifier OP_M to the detection coil 12. With this configuration, the magnetic field B IN When the feedback current I FB The detection coil 12 detects the magnetic field B IN The feedback magnetic field B to cancel FB If the feedback magnetic field B FB is the magnetic field to be detected B IN When the two are completely offset, the feedback current I FB or feedback voltage V FB is the magnetic field to be detected B IN In other words, the return magnetic field B FB is the magnetic field to be detected B IN If it can be completely canceled, the feedback current I FB , or the feedback current I FB By detecting the physical quantity corresponding to the target magnetic field B IN can be detected.

[0105] Return magnetic field B FB is the magnetic field to be detected B IN In the state where the magnetic field B is cancelled out, the magnetic field is not acting on the magnetic sensitive body 11. IN The feedback current I FB does not depend on the electromagnetic characteristics of the magnetosensitive body 11.IN and the feedback current I FB Therefore, the relationship between the feedback current I FB or the feedback current I FB By detecting the physical quantity corresponding to the target magnetic field B IN The detection accuracy can be improved.

[0106] Furthermore, according to the magnetic detection device 1 of this embodiment, both ends of the detection coil 12 of the MI sensor element 2 are connected to the inverting input terminal and the non-inverting input terminal of the main operational amplifier OP_M. Furthermore, the magnetic detection device 1 includes two feedback circuits 25, 26. One of the two feedback circuits 25, 26 is a first feedback circuit 25 connected between the output terminal of the main operational amplifier OP_M and the first end 12a of the detection coil 12. The other of the two feedback circuits 25, 26 is a second feedback circuit 26 connected between the output terminal of the main operational amplifier OP_M and the second end 12b of the detection coil 12.

[0107] With this configuration, the feedback current I FB is the first feedback voltage V generated by the first feedback circuit 25. FB1 and the second feedback voltage V generated by the second feedback circuit 26. FB2 The current is proportional to the potential difference ΔVx between the feedback current I FB The physical quantity corresponding to, for example, the first feedback voltage V FB1 and the second feedback voltage V FB2 The potential difference between the positive and negative terminals can be expressed as ΔVx.

[0108] And the second feedback voltage V FB2 is the first feedback voltage V FB1 In particular, the second feedback voltage V FB2 is the first feedback voltage V FB1 is an inverted voltage with respect to a predetermined reference voltage VB. Therefore, the first feedback voltage V FB1 and the second feedback voltage V FB2 In other words, the feedback current I FBAnd the feedback current I FB In order to increase the feedback current I FB It does not reduce the resistance of the circuit through which it flows, nor does it increase the power supply voltage.

[0109] As described above, according to this embodiment, when the feedback circuits 25 and 26 are provided, the feedback current I FB The feedback current I flows through the detection coil 12 without decreasing the resistance of the circuit through which it flows and without increasing the power supply voltage. FB It is possible to provide a magnetic detection device 1 capable of increasing the

[0110] (Embodiment 2) The magnetic detection device 1 of this embodiment will be described with reference to Fig. 7. The magnetic detection device 1 of this embodiment includes an MI sensor element 2 and a detection circuit 4. The detection circuit 4 includes a common feedback input voltage generating circuit 29 in addition to the detection circuit 3 of the first embodiment.

[0111] Other than the common feedback input voltage generating circuit 29, the configuration is the same as that of the first embodiment. The detection circuit 4 includes a signal output unit 27 and a reference power supply 28, similar to the detection circuit 3 of the first embodiment, but these are omitted in Fig. 7. Note that, among the symbols used in the second embodiment, those that are the same as those used in the previous embodiments represent the same components, etc., as those in the previous embodiments, unless otherwise specified.

[0112] The common feedback input voltage generating circuit 29 (hereinafter simply referred to as "generating circuit 29") is connected to the output terminal of the main operational amplifier OP_M, and performs at least one of phase adjustment processing, differentiation processing, and integration processing on the output voltage of the main operational amplifier OP_M. The generating circuit 29 generates a common feedback input voltage for the first feedback circuit 25 and the second feedback circuit 26. That is, the generating circuit 29 is connected to the inverting input terminal of the first feedback operational amplifier OP_FB1 constituting the first feedback circuit 25, and the non-inverting input terminal of the second feedback operational amplifier OP_FB2 constituting the second feedback circuit 26.

[0113] The generation circuit 29 is configured with an operational amplifier OP_S. The generation circuit 29 is configured to include resistors R13 and R14 and capacitors C5 and C6 depending on the intended function. The operational amplifier OP_S is configured with a single power supply operational amplifier.

[0114] According to this embodiment, when generating a voltage that has undergone the above-mentioned processing as an input voltage to the first feedback circuit 25 and the second feedback circuit 26, the circuit configuration can be simplified by providing one generation circuit 29 compared to the case where separate generation circuits are provided. Furthermore, this embodiment also has the same effects as the first embodiment.

[0115] When the generating circuit 29 is a circuit that performs differentiation and integration, the phase of the input / output signals is inverted by 180°. In this case, it is preferable that the non-inverting input terminal of the main operational amplifier OP_M is connected to the first end 12a of the detection coil 12, and the inverting input terminal is connected to the second end 12b of the detection coil 12.

[0116] (others) In the first and second embodiments, the operational amplifiers OP_M, OP_FB1, OP_FB2, and OP_S are configured as single-power operational amplifiers, but they may be configured as dual-power operational amplifiers. In this case, the predetermined reference voltage VB may be set to be close to the ground potential instead of a positive voltage.

[0117] In the first embodiment, the first feedback circuit 25 and the second feedback circuit 26 are directly connected to the output terminal of the main amplifier circuit 22. Alternatively, they may be connected via an AD conversion circuit and a DA conversion circuit, which allows digital signal processing to be performed. [Explanation of symbols]

[0118] 1 Magnetic detection device 2. Magneto-impedance sensor element (MI sensor element) 12 Detection coil 12a First end of detection coil 12b Second end of detection coil 25 First feedback circuit 26 Second feedback circuit OP_M Main operational amplifier V FB1 First Feedback Voltage V FB2 Second Feedback Voltage VB Predetermined reference voltage

Claims

1. a magneto-impedance sensor element including a magneto-sensitive body that undergoes a magnetization change corresponding to the strength of a magnetic field when an excitation current is supplied thereto, and a detection coil wound around the magneto-sensitive body and outputting an induced voltage generated by the magnetization change of the magneto-sensitive body; a main operational amplifier having one of an inverting input terminal and a non-inverting input terminal connected to a first end of the detection coil, and the other of the inverting input terminal and the non-inverting input terminal connected to a second end of the detection coil opposite to the first end; a first feedback circuit connected between an output terminal of the main operational amplifier and the first end of the detection coil, for generating a first feedback voltage for generating a feedback current in the detection coil; a second feedback circuit connected between the output terminal of the main operational amplifier and the second end of the detection coil, the second feedback circuit generating a second feedback voltage having a polarity inverted with respect to the first feedback voltage when a predetermined reference voltage is used as a reference, in order to generate the feedback current in the detection coil; A magnetic detection device comprising:

2. the first feedback circuit includes a first feedback operational amplifier having an input terminal connected to an output terminal side of the main operational amplifier and an output terminal connected to the first end side of the detection coil, the second feedback circuit includes a second feedback operational amplifier having an input terminal connected to an output terminal side of the main operational amplifier and an output terminal connected to the second end side of the detection coil, the first feedback voltage is a voltage at an output terminal of the first feedback operational amplifier, the second feedback voltage is a voltage at an output terminal of the second feedback operational amplifier, 2. The magnetic detection device according to claim 1, wherein an input terminal of the first feedback operational amplifier is connected to the output terminal side of the main operational amplifier, and an input terminal of the second feedback operational amplifier is connected to the output terminal side of the main operational amplifier, one of the input terminals being an inverting input terminal and the other being a non-inverting input terminal.

3. The amplification factor of the first feedback circuit and the amplification factor of the second feedback circuit are set to be the same, 3. The magnetic detection device according to claim 2, wherein the second feedback voltage is an inverted voltage of the first feedback voltage when the predetermined reference voltage is used as a reference.

4. The first feedback circuit includes: the first feedback operational amplifier; a first impedance circuit connected between an output terminal of the first feedback operational amplifier and the first end of the detection coil, the first impedance circuit suppressing the induced voltage output by the detection coil from moving toward the first feedback operational amplifier; Equipped with The second feedback circuit includes: The second feedback operational amplifier; a second impedance circuit connected between an output terminal of the second feedback operational amplifier and the second end of the detection coil, the second impedance circuit suppressing the induced voltage output by the detection coil from moving toward the second feedback operational amplifier; The magnetic detection device according to claim 2 or 3, comprising:

5. 5. The magnetic detection device according to claim 4, wherein the impedance of the first impedance circuit and the impedance of the second impedance circuit are set to be the same.

6. The magnetic detection device according to any one of claims 1 to 5, further comprising a common feedback input voltage generation circuit connected to an output terminal of the main operational amplifier, performing at least one of a phase adjustment process, a differentiation process, and an integration process on an output voltage of the main operational amplifier, and generating a common feedback input voltage for the first feedback circuit and the second feedback circuit.

7. moreover, a first input circuit connected between the first end of the detection coil and the inverting input terminal of the main operational amplifier, holding a voltage at the first end at a predetermined timing and inputting the held voltage at the first end to the inverting input terminal of the main operational amplifier; a second input circuit connected between the second end of the detection coil and the non-inverting input terminal of the main operational amplifier, holding a voltage of the second end at a timing identical to the predetermined timing, and inputting the held voltage of the second end to the non-inverting input terminal of the main operational amplifier; The magnetic detection device according to any one of claims 1 to 6, comprising:

8. 8. The magnetic detection device according to claim 1, wherein the predetermined reference voltage is a positive voltage.

9. 9. The magnetic detection device according to claim 8, further comprising a common reference power supply that applies the positive voltage as the predetermined reference voltage to the first feedback circuit and the second feedback circuit.

10. The magnetic detection device according to any one of claims 1 to 9, further comprising a signal output unit that outputs a potential difference between the first feedback voltage and the second feedback voltage, or the feedback current, as a detection signal representing the strength of the magnetic field to be detected acting on the magnetic sensitive body.

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