High-bandwidth current detection circuit based on TMR

Abstract

The invention provides a high-bandwidth current detection circuit based on TMR. The high-bandwidth current detection circuit comprises a voltage sensing circuit, a zeroing circuit, a first amplifying circuit and a second amplifying circuit. The voltage sensing circuit is used for sensing a surrounding magnetic field, converting a sensed magnetic field signal into a differential voltage signal and sending the differential voltage signal to the zeroing circuit, the first amplifying circuit and the second amplifying circuit. The first amplification circuit and the second amplification circuit are used for amplifying the differential voltage signal and then outputting the amplified differential voltage signal, and the zeroing circuit is used for carrying out zeroing on the differential voltage signal initially, so that the output voltage of the first amplification circuit and the second amplification circuit is zero when the detection current is zero. The magnetic field change sensed by the magnetic resistance element L1 is converted into a voltage signal, the signal is amplified through zero setting and the two-stage amplification circuit, and finally a differential voltage signal in a linear relation with the magnitude of the measured current is output. The positive and negative values of the differential signal not only can represent the direction of the current, but also effectively improve the anti-interference capability, so that the circuit can adapt to a complex electromagnetic environment.

Description

Technical Field

[0001] The present invention relates to the field of current detection circuits, and more particularly to a high-bandwidth current detection circuit based on TMR. Background Art

[0002] Common current detection methods include using Hall sensors, CT devices, etc., which pass the conductor through which the measured current flows through the window of the Hall sensor or CT device. The Hall sensor or CT device converts the measured current into a small voltage or current signal according to the corresponding ratio. When detecting large currents, it has the characteristics of large size and complex installation.

[0003] Hall current sensors can be divided into two types, one is open loop (direct type) and the other is closed loop (magnetic balance type). Hall current sensor is a magnetic field sensor made based on the Hall effect. The accuracy and linearity of open-loop Hall sensors are poor, the response time is slow, the temperature drift is large, and the bandwidth is small. Closed-loop Hall sensors optimize most of the shortcomings of switch Hall sensors, and the cost is higher than that of open-loop Hall sensors.

[0004] Based on this, a new solution is needed that can meet the requirements of measuring high bandwidth, large current, low cost and flexible current measurement. Summary of the invention

[0005] The purpose of the present invention is to provide a high-bandwidth current detection circuit based on TMR to replace the Hall sensor sampling method, which has the advantages of low cost, reliable circuit, small size, easy installation and strong adaptability, etc., in view of the shortcomings of existing Hall sensors such as high price, relatively small open-loop bandwidth, complex installation and fixed measurement range of finished Hall.

[0006] According to one aspect of the present invention, a high-bandwidth current detection circuit based on TMR is provided, comprising a voltage sensing circuit, a zeroing circuit, a first amplifier circuit and a second amplifier circuit, wherein the first output end of the voltage sensing circuit is connected to the first input end of the zeroing circuit and the first input end of the first amplifier circuit, the second output end of the voltage sensing circuit is connected to the second input end of the zeroing circuit and the first input end of the first amplifier circuit, the voltage sensing circuit is used to sense the surrounding magnetic field and convert the sensed magnetic field signal into a differential voltage signal and send it to the zeroing circuit, the first amplifier circuit and the second amplifier circuit; the first amplifier circuit and the second amplifier circuit are used to amplify the differential voltage signal and then output it, and the zeroing circuit is used to initially zero the differential voltage signal so that the output voltages of the first amplifier circuit and the second amplifier circuit are zero.

[0007] In the TMR-based high-bandwidth current detection circuit provided by the present invention, the voltage sensing circuit includes a magnetoresistive element L1, a capacitor C1 and a capacitor C4, the VDD end of the magnetoresistive element L1 is connected to the first end of the capacitor C1 and the first end of the capacitor C4, the GND end of the magnetoresistive element L1 is connected to the second end of the capacitor C1 and the second end of the capacitor C4, the X1 end of the magnetoresistive element L1 is the first output end of the voltage sensing circuit, and the X2 end of the magnetoresistive element L1 is the second output end of the voltage sensing circuit.

[0008] In the TMR-based high-bandwidth current detection circuit provided by the present invention, the zero adjustment circuit includes a dip switch SW1, a resistor R8 and a resistor R9, the first and second dip positions of the dip switch SW1 are connected to the X1 end of the magnetic resistance element L1, the third and fourth dip positions of the dip switch SW1 are connected to the X2 end of the magnetic resistance element L1, the sixth and eighth dip positions of the dip switch SW1 are connected to the first end of the resistor R8, the fifth and seventh dip positions of the dip switch SW1 are connected to the first end of the resistor R9, the second end of the resistor R8 is connected to the external voltage, and the second end of the resistor R9 is grounded.

[0009] In the TMR-based high-bandwidth current detection circuit provided by the present invention, initially, if it is detected that the difference between the output voltage of the first amplifier circuit and the output voltage of the second amplifier circuit is positive, the first dial position and the eighth dial position are closed and the second dial position and the seventh dial position are closed; if it is detected that the difference between the output voltage of the first amplifier circuit and the output voltage of the second amplifier circuit is negative, the third dial position and the sixth dial position are closed and the fourth dial position and the fifth dial position are closed.

[0010] In the TMR-based high-bandwidth current detection circuit provided by the present invention, the first amplification circuit includes an operational amplifier U1, a capacitor C2, a capacitor C3, a capacitor C5, a resistor R2 and a resistor R4, the positive input end of the operational amplifier U1 is connected to the X1 end of the magnetoresistive element L1, the reverse input end of the operational amplifier U1 is connected to the first end of the capacitor C5 and the first end of the resistor R2, the output end of the operational amplifier U1 is connected to the second end of the capacitor C5, the second end of the resistor R2 and the first end of the resistor R4, the second end of the resistor R4 is the first differential output end, and the capacitor C2 and the capacitor C3 are connected in parallel between the positive power supply end and the negative power supply end of the operational amplifier U1.

[0011] In the TMR-based high-bandwidth current detection circuit provided by the present invention, the second amplification circuit includes an operational amplifier U2, a capacitor C6, a resistor R1, a resistor R3 and a resistor R5, the positive input end of the operational amplifier U2 is connected to the X2 end of the magnetoresistive element L1, the reverse input end of the operational amplifier U2 is connected to the first end of the capacitor C6, the first end of the resistor R3 and the first end of the resistor R1, the output end of the operational amplifier U2 is connected to the second end of the capacitor C6, the second end of the resistor R3 and the first end of the resistor R5, the second end of the resistor R5 is a second differential output end, and the second end of the resistor R1 is connected to the reverse input end of the operational amplifier U1.

[0012] The implementation of the TMR-based high-bandwidth current detection circuit of the present invention has the following beneficial effects: the TMR-based high-bandwidth current detection circuit provided by the present invention converts the magnetic field change sensed by the magnetoresistive element L1 into a voltage signal, and then amplifies the signal through zero adjustment and two operational amplifiers to form an instrument amplifier circuit, and finally outputs a differential voltage signal that is linearly related to the magnitude of the measured current; utilizing the characteristics of the differential signal, the positive and negative values ​​of the differential signal can not only indicate the direction of the current, but also effectively improve the anti-interference ability, so that the circuit can adapt to complex electromagnetic environments and is widely used in high-precision, large current measurement and monitoring systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings in the following description are only embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on the provided drawings without creative work:

[0014] Figure 1 FIG. 1 is a schematic diagram of a high-bandwidth current detection circuit based on TMR proposed by the present invention;

[0015] Figure 2 Shown is a circuit diagram of a TMR-based high-bandwidth current detection circuit proposed by the present invention. DETAILED DESCRIPTION

[0016] In order to facilitate understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0018] Figure 1 FIG. 1 is a schematic diagram of a high bandwidth current detection circuit based on TMR proposed by the present invention. Figure 1 As shown, the TMR-based high-bandwidth current detection circuit provided by the present invention includes a voltage sensing circuit 10, a zeroing circuit 20, a first amplifier circuit 30 and a second amplifier circuit 40. The voltage sensing circuit 10 is used to sense the surrounding magnetic field and convert the sensed magnetic field signal into a differential voltage signal, and the converted differential voltage signal is sent to the zeroing circuit 20, the first amplifier circuit 30 and the second amplifier circuit 40 connected thereto through the first output terminal and the second output terminal respectively. Due to the difference in the process of the internal magnetic resistance and the influence of the geomagnetism, there will be a zero current offset voltage Voffset in the voltage sensing circuit, that is, when the external current is 0A, there will be a bias voltage in the voltage Vo between Io+ and Io-. Therefore, at the initial time (that is, when the detection current is 0), the differential voltage signal is zeroed by the zeroing circuit so that the output voltage of the first amplifier circuit and the second amplifier circuit is zero when the detection current is zero; then the differential voltage signal is amplified and output by the first amplifier circuit 30 and the second amplifier circuit 40.

[0019] Specifically, in one embodiment of the present invention, Figure 2As shown, the voltage sensing circuit includes a magnetoresistive element L1, a capacitor C1 and a capacitor C4. In this embodiment, the magnetoresistive element L1 uses the tunnel magnetoresistance effect (TMR) to sense the change of the external magnetic field and convert it into a voltage signal. The resistance value of the magnetoresistive element will change with the change of the magnetic field strength, thereby affecting the voltage in the circuit. The magnetoresistive element L1 has four terminals: VDD terminal, GND terminal, X1 terminal and X2 terminal. Among them, the VDD terminal is connected to the first end of the capacitor C1 and the capacitor C4 to provide the power supply voltage; the GND terminal is connected to the second end of the capacitor C1 and the capacitor C4 as the ground terminal of the circuit; the X1 terminal and the X2 terminal are the output terminals of the voltage sensing circuit, and the voltage signal is obtained through these two ports. The VDD terminal and the GND terminal are connected through the capacitor C1 and the capacitor C4, which can enhance the stability of the power supply and reduce the influence of the power supply noise on the voltage sensing circuit. During detection, the resistance of the magnetoresistive element L1 changes under the influence of the external magnetic field. Through the X1 terminal and the X2 terminal of the magnetoresistive element L1, the circuit can output a differential voltage signal, which is proportional to the magnetic field generated by the external current. Based on the magnetoresistance effect, the magnetic field change is sensed by the magnetoresistance element L1, and a differential voltage signal proportional to the current is generated through the output terminals (X1, X2).

[0020] In the present embodiment, TMR technology is adopted, based on the principle that the resistance of magnetic materials changes under the influence of external magnetic fields, so by monitoring the magnetic field changes caused by external current, a voltage signal proportional to the current size and direction can be obtained. Since the output is a differential signal, compared with the ordinary single-ended voltage output, the anti-interference ability, signal quality, transmission distance and measurement accuracy of the voltage sensing circuit can be significantly improved. By using TMR elements as magnetic field sensing elements, it can work within a higher bandwidth range, which makes it have better performance in rapidly changing current detection occasions. When installed and used, different measurement ranges can be achieved by adjusting the distance and angle with the measured current wire or conductor, and it has the characteristics of high accuracy, fast response, and electrical isolation with the measured signal. At the same time, the capacitor helps stabilize the power supply voltage and improves the anti-interference ability of the circuit.

[0021] Specifically, in one embodiment of the present invention, Figure 2As shown, the zero adjustment circuit includes a dial switch SW1, a resistor R8 and a resistor R9, wherein the resistor R8 and the resistor R9 are used for pull-up and pull-down, and a DC component is superimposed on the output signal of L1. The dial switch SW1 is used to select the increase or decrease of the DC component, and R8 and R9 can adjust the DC component. The first and second dial positions of the dial switch SW1 are connected to the X1 end of the magnetic resistance element L1, the third and fourth dial positions of the dial switch SW1 are connected to the X2 end of the magnetic resistance element L1, the sixth and eighth dial positions of the dial switch SW1 are connected to the first end of the resistor R8, the fifth and seventh dial positions of the dial switch SW1 are connected to the first end of the resistor R9, the second end of the resistor R8 is connected to the external voltage, and the second end of the resistor R9 is grounded. Different dial positions of the dial switch SW1 are respectively connected to the X1 and X2 ends of L1, and different terminals of R8 and R9. By adjusting different dial positions of SW1, different paths and different resistance values ​​can be selected to adjust the increase or decrease of the DC component. Initially, if it is detected that the difference between the output voltage of the first amplifier circuit and the output voltage of the second amplifier circuit is positive, the first dial position and the eighth dial position are closed and the second dial position and the seventh dial position are closed; if it is detected that the difference between the output voltage of the first amplifier circuit and the output voltage of the second amplifier circuit is negative, the third dial position and the sixth dial position are closed and the fourth dial position and the fifth dial position are closed.

[0022] In the present embodiment, the working principle of the zero adjustment circuit is mainly to adjust the output signal of the magnetoresistive element L1 through the code switch (SW1) and the resistor (R8 and R9) to compensate for the zero current bias voltage (Voffset) caused by process differences, geomagnetism and other factors. When there is a bias voltage in the output of L1, the output signal of L1 can be accurately adjusted by adjusting SW1 and R8, R9 to achieve the effect of zero current compensation. Specifically, the magnetoresistive element L1 may generate a zero current bias voltage (Voffset) due to manufacturing process differences and external environment (such as geomagnetic field) during operation. Even when the external current is 0, the output signal (Vo) of L1 may also have a bias voltage. When Vo is positive, the 1st and 2nd bits of the code switch SW1 are set to 1, and the 3rd and 4th bits are set to 0. At this time, the signal is output through the X1 end of L1, and a DC voltage is superimposed on this end to compensate for the bias voltage. Appropriate resistors R8 and R9 can accurately adjust the size of the DC voltage to achieve compensation of the bias voltage. When Vo is negative, the 3rd and 4th bits of the code switch SW1 are set to 1, and the 1st and 2nd bits are set to 0. At this time, the signal is output through the X2 terminal of L1, and a DC voltage is superimposed on this terminal for compensation. The DC voltage can also be adjusted by appropriate resistors R8 and R9 to finally achieve the effect of zero adjustment. In practical applications, the zero adjustment circuit can achieve zero adjustment operation through a simple code switch without replacing the device, which simplifies the operation process and improves efficiency. According to the specification and requirements of L1, select the appropriate resistance value (R8 and R9), and adjust the setting of the code switch SW1 to conveniently zero L1 to ensure that it can output accurate signals during use. The zero adjustment circuit can compensate for the zero current bias of the magnetoresistive element L1 by using the code switch SW1 and appropriate resistors R8 and R9, solve the bias problem caused by internal process differences and external environmental changes, achieve precise zero adjustment, improve the stability and reliability of the circuit, avoid the trouble of replacing components, and make the operation more convenient.

[0023] Specifically, in one embodiment of the present invention, Figure 2As shown, the first amplifier circuit includes an operational amplifier U1, a capacitor C2, a capacitor C3, a capacitor C5, a resistor R2 and a resistor R4, the positive input end of the operational amplifier U1 is connected to the X1 end of the magnetoresistive element L1, the reverse input end of the operational amplifier U1 is connected to the first end of the capacitor C5 and the first end of the resistor R2, the output end of the operational amplifier U1 is connected to the second end of the capacitor C5, the second end of the resistor R2 and the first end of the resistor R4, the second end of the resistor R4 is the first differential output end, and the capacitor C2 and the capacitor C3 are connected in parallel between the positive power supply end and the negative power supply end of the operational amplifier U1. Capacitor C5 and resistor R2 form a feedback path to help control the gain of the amplifier circuit. The second end of resistor R4 is connected to the first differential output end, which plays a role in current limiting protection and ensures that the signal is transmitted within an appropriate range. Capacitors C2 and C3 are connected in parallel between the positive and negative power supply ends of the operational amplifier U1 to provide decoupling, reduce the influence of power supply noise, and ensure stable operation of the circuit.

[0024] Specifically, in one embodiment of the present invention, Figure 2 As shown, the second amplifier circuit includes an operational amplifier U2, a capacitor C6, a resistor R1, a resistor R3 and a resistor R5. The positive input terminal of the operational amplifier U2 is connected to the X2 terminal of the magnetoresistive element L1. X2 is another output terminal of L1, which outputs a voltage signal related to the change of the magnetic field. In cooperation with the X1 terminal, X1 and X2 form a differential output signal of L1. The reverse input terminal of the operational amplifier U2 is connected to the first terminal of the capacitor C6, the first terminal of the resistor R3 and the first terminal of the resistor R1. These components form a feedback loop to adjust the gain and stability. The output terminal of the operational amplifier U2 is connected to the second terminal of the capacitor C6, the second terminal of the resistor R3 and the first terminal of the resistor R5. The function of the capacitor C6 is to filter and remove high-frequency noise to ensure the quality of the output signal. The second terminal of the resistor R5 is connected to the second differential output terminal to limit the current output and protect the circuit. The second end of the resistor R1 is connected to the reverse input terminal of the operational amplifier U1 to form a differential input, so that the two amplifier circuits can work together and finally output the differential voltage signal of L1.

[0025] In this embodiment, the first amplifier circuit U1 and the second amplifier circuit U2 respectively amplify the voltage signals from the two endpoints (X1 and X2) of L1. Since the voltage output from the two ports of L1 is differential, the two operational amplifiers enhance the signal by differential amplification, thereby enhancing the circuit's sensitivity to signal changes. Capacitors (such as C5 and C6) and resistors (such as R2, R3, etc.) jointly affect the gain and the frequency response of the amplifier circuit, and also play a role in denoising and filtering, reducing the impact of external interference on the amplified signal. Resistors R4 and R5 play a role in current limiting protection, preventing damage to the operational amplifier due to excessive current, and also help control the range of the output signal to ensure that the signal output meets the design requirements.

[0026] The high-bandwidth current detection circuit based on TMR provided by the present invention senses the magnetic field generated by the measured current based on the magnetoresistive element L1, and converts it into a voltage signal, and finally outputs a differential voltage signal that is linearly related to the measured current. Through the differential signal, the magnitude and direction of the measured current can be obtained, and the anti-interference ability is enhanced at the same time to adapt to complex electromagnetic environments. The signal of L1 can be zeroed by the zeroing circuit to ensure that the output signal is still close to zero voltage even in the absence of an external magnetic field (or the current is zero). The voltage signal sensed by L1 is generally weak and cannot be used directly for monitoring. Therefore, the signal is amplified by the operational amplifier of the subsequent stage. By adjusting the gain of the amplifier circuit, a stronger voltage signal can be obtained, which is convenient for subsequent processing and output. At the same time, compared with the single-ended signal, the differential signal can significantly improve the circuit's resistance to common-mode interference. In a complex electromagnetic environment, power supply noise, ground line noise, etc. often affect the circuit through the ground line or power supply line, and the differential signal can effectively eliminate the influence of such noise. The differential signal usually uses two-wire transmission (positive and negative ends are symmetrical), which can avoid interference introduced by external electromagnetic fields. Even in an environment with strong electromagnetic interference, differential signals can maintain high signal quality and adapt to more complex electromagnetic environments.

[0027] In each of the descriptions provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0028] Similarly, it should be understood that in order to streamline the present disclosure and aid in understanding one or more of the various inventive aspects, in the above description of exemplary embodiments of the present invention, various features of the present invention are sometimes grouped together into a single embodiment, figure, or description thereof. However, this disclosed method should not be interpreted as reflecting the intention that the claimed invention requires more features than those explicitly recited in each claim. More specifically, as reflected in the claims below, inventive aspects lie in less than all the features of the individual embodiments disclosed above. Therefore, the claims that follow the specific embodiment are hereby expressly incorporated into the specific embodiment, with each claim itself serving as a separate embodiment of the present invention.

[0029] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and form different embodiments. For example, in the claims below, any one of the claimed embodiments may be used in any combination.

[0030] It should be noted that the above embodiments illustrate the present invention rather than limit it, and that those skilled in the art may devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference symbol between brackets shall not be construed as a limitation on the claims. The word "comprising" does not exclude the presence of elements or steps not listed in the claims. The word "one" or "an" preceding an element does not exclude the presence of a plurality of such elements. The present invention may be implemented by means of hardware comprising a number of different elements and by means of a suitably programmed computer. In a unit claim enumerating a number of devices, several of these devices may be embodied by the same hardware item. The use of the words first, second, and third, etc., does not indicate any order. These words may be interpreted as names.

Claims

1. A high bandwidth current detection circuit based on TMR, characterized in that: It includes a voltage sensing circuit, a zeroing circuit, a first amplifier circuit and a second amplifier circuit. The first output end of the voltage sensing circuit is connected to the first input end of the zeroing circuit and the first input end of the first amplifier circuit. The second output end of the voltage sensing circuit is connected to the second input end of the zeroing circuit and the first input end of the first amplifier circuit. The voltage sensing circuit is used to sense the surrounding magnetic field and convert the sensed magnetic field signal into a differential voltage signal and send it to the zeroing circuit, the first amplifier circuit and the second amplifier circuit; the first amplifier circuit and the second amplifier circuit are used to amplify the differential voltage signal and then output it. The zeroing circuit is used to zero the differential voltage signal at the initial stage so that the output voltage of the first amplifier circuit and the second amplifier circuit is zero when the detection current is zero.

2. The TMR-based high-bandwidth current detection circuit according to claim 1, characterized in that: The voltage sensing circuit includes a magnetoresistive element L1, a capacitor C1 and a capacitor C4, the VDD end of the magnetoresistive element L1 is connected to the first end of the capacitor C1 and the first end of the capacitor C4, the GND end of the magnetoresistive element L1 is connected to the second end of the capacitor C1 and the second end of the capacitor C4, the X1 end of the magnetoresistive element L1 is the first output end of the voltage sensing circuit, and the X2 end of the magnetoresistive element L1 is the second output end of the voltage sensing circuit.

3. The TMR-based high-bandwidth current detection circuit according to claim 2, characterized in that: The zero adjustment circuit includes a dip switch SW1, a resistor R8 and a resistor R9. The first and second dip positions of the dip switch SW1 are connected to the X1 end of the magnetoresistive element L1, the third and fourth dip positions of the dip switch SW1 are connected to the X2 end of the magnetoresistive element L1, the sixth and eighth dip positions of the dip switch SW1 are connected to the first end of the resistor R8, the fifth and seventh dip positions of the dip switch SW1 are connected to the first end of the resistor R9, the second end of the resistor R8 is connected to an external voltage, and the second end of the resistor R9 is grounded.

4. The TMR-based high-bandwidth current detection circuit according to claim 3, characterized in that: Initially, if it is detected that the difference between the output voltage of the first amplifier circuit and the output voltage of the second amplifier circuit is positive, the first dial position and the eighth dial position are closed, and the second dial position and the seventh dial position are closed; If it is detected that the difference between the output voltage of the first amplifier circuit and the output voltage of the second amplifier circuit is negative, the third dial bit and the sixth dial bit are closed, and the fourth dial bit and the fifth dial bit are closed.

5. The TMR-based high-bandwidth current detection circuit according to claim 2, characterized in that: The first amplifier circuit includes an operational amplifier U1, a capacitor C2, a capacitor C3, a capacitor C5, a resistor R2 and a resistor R4, the positive input terminal of the operational amplifier U1 is connected to the X1 terminal of the magnetoresistive element L1, the reverse input terminal of the operational amplifier U1 is connected to the first end of the capacitor C5 and the first end of the resistor R2, the output terminal of the operational amplifier U1 is connected to the second end of the capacitor C5, the second end of the resistor R2 and the first end of the resistor R4, the second end of the resistor R4 is a first differential output terminal, and the capacitor C2 and the capacitor C3 are connected in parallel between the positive power supply terminal and the negative power supply terminal of the operational amplifier U1.

6. The TMR-based high-bandwidth current detection circuit according to claim 5, characterized in that: The second amplifier circuit includes an operational amplifier U2, a capacitor C6, a resistor R1, a resistor R3 and a resistor R5, the positive input terminal of the operational amplifier U2 is connected to the X2 terminal of the magnetoresistive element L1, the reverse input terminal of the operational amplifier U2 is connected to the first end of the capacitor C6, the first end of the resistor R3 and the first end of the resistor R1, the output terminal of the operational amplifier U2 is connected to the second end of the capacitor C6, the second end of the resistor R3 and the first end of the resistor R5, the second end of the resistor R5 is a second differential output terminal, and the second end of the resistor R1 is connected to the reverse input terminal of the operational amplifier U1.

Images