Tunneling magnetoresistive sensing circuit

Abstract

The invention provides a tunneling magnetoresistive sensing circuit. The tunneling magnetoresistive sensing circuit comprises a band-gap reference circuit for providing reference voltage; two input ends of the operational transconductance amplifier are respectively connected with a reference voltage and a source electrode of the MOS tube, and an output end of the operational transconductance amplifier is connected with a grid electrode of the MOS tube so as to perform negative feedback on a bias current output by the source electrode of the MOS tube; the drain electrode of the MOS tube is connected with power supply voltage, and the source electrode of the MOS tube is connected with the tunneling magnetoresistive sensor so as to provide bias current for the tunneling magnetoresistive sensor; the reference voltage is changed to change a temperature coefficient of the bias current. Bias current with a certain temperature coefficient is provided through the band-gap reference circuit, the operational transconductance amplifier and the MOS tube, and the sensitivity temperature coefficient of the tunneling magnetoresistive sensor is compensated, so that the tunneling magnetoresistive sensor is not easy to generate measurement deviation due to temperature influence; therefore, the tunneling magnetoresistive sensor can be well applied to application scenes with a wide working temperature range and high precision requirements, and the problem that an existing tunneling magnetoresistive sensor is prone to being affected by temperature to generate measurement deviation is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of circuits, and particularly to a tunneling magnetoresistance sensing circuit. Background Art

[0002] A tunneling magnetoresistance (TMR) sensor is used to detect weak magnetic fields and convert magnetic field signals into electrical signals that are easy to process. It has excellent performance in terms of sensitivity, temperature stability, anti-interference ability, miniaturization, integration, intelligence, and low power consumption. Therefore, it has good application prospects.

[0003] In application scenarios with low requirements for measurement accuracy, traditional bias-operated TMR sensors can meet the working requirements. However, with the development of technologies such as automation technology, household appliances, and satellite positioning, the requirements for magnetoresistance sensors are becoming increasingly stringent, and it is required that TMR sensors can handle precise measurement requirements in various working environments. In some application scenarios where the working environment temperature changes greatly (for example, in high-altitude areas where the temperature difference between seasons and day and night is large), traditional TMR will produce large measurement deviations. For example, a TMR sensor with a sensitivity temperature coefficient of 900 ppm / °C will produce a measurement deviation of about 12.6% under a temperature change from -40°C to 100°C. This measurement deviation may cause the system to have different judgments for the same sensing input, resulting in malfunction. Summary of the Invention

[0004] The purpose of the present invention is to provide a tunneling magnetoresistance sensing circuit to solve the problem that existing tunneling magnetoresistance sensors are easily affected by temperature and produce measurement deviations.

[0005] To solve the above technical problems, the present invention provides a tunneling magnetoresistance sensing circuit, including a bandgap reference circuit, an operational transconductance amplifier, an MOS transistor, and a tunneling magnetoresistance sensor; the bandgap reference circuit is used to provide a reference voltage; the first input terminal of the operational transconductance amplifier is connected to the reference voltage, the second input terminal is connected to the source electrode of the MOS transistor, and the output terminal is connected to the gate electrode of the MOS transistor to perform negative feedback on the bias current output from the source electrode of the MOS transistor; the drain electrode of the MOS transistor is connected to the power supply voltage, and the source electrode is connected to the tunneling magnetoresistance sensor to provide a bias current for the tunneling magnetoresistance sensor; by changing the reference voltage, the temperature coefficient of the bias current is changed.

[0006] Optionally, in the tunneling magnetoresistance sensing circuit, the tunneling magnetoresistance sensing circuit further includes a chopper circuit; the chopper circuit is arranged before the first input terminal and the second input terminal of the operational transconductance amplifier to reduce noise of the reference voltage input to the first input terminal and the bias current input to the second input terminal.

[0007] Optionally, in the tunneling magnetoresistance sensing circuit, the bandgap reference circuit includes a first transistor, a second transistor, a third transistor, a fourth transistor, an operational amplifier, a first triode, a second triode, a first resistor, a second resistor, a third resistor, a fourth resistor, and a fifth resistor; The sources of the first transistor, the second transistor, the third transistor, and the fourth transistor are connected to a power supply voltage, and their gates are connected; the drain of the first transistor is connected to the first input terminal of the operational amplifier, the first end of the first resistor, and the emitter of the first triode; the drain of the second transistor is connected to the second input terminal of the operational amplifier, the first end of the second resistor, and the first end of the third resistor; the drain of the third transistor is connected to the first end of the fourth resistor; the drain of the fourth transistor is connected to the first end of the fifth resistor, and an output terminal of the reference voltage is led out; the output terminal of the operational amplifier is connected to the gate of the first transistor; the second end of the first resistor is connected to an equipotential; the base and the collector of the first triode are short-circuited and connected to an equipotential; the second end of the second resistor is connected to the emitter of the second triode; the base and the collector of the second triode are short-circuited and connected to an equipotential; the second ends of the third resistor, the fourth resistor, and the fifth resistor are all connected to an equipotential.

[0008] Optionally, in the tunneling magnetoresistance sensing circuit, the bandgap reference circuit further includes a first filter circuit and a second filter circuit; the drain of the first transistor is connected to the first input terminal of the operational amplifier, the first end of the first resistor, and the emitter of the first triode through the first filter circuit; the drain of the second transistor is connected to the second input terminal of the operational amplifier, the first end of the second resistor, and the first end of the third resistor through the first filter circuit; the drain of the third transistor is connected to the first end of the fourth resistor through the second filter circuit; the drain of the fourth transistor is connected to the first end of the fifth resistor through the second filter circuit.

[0009] Optionally, in the tunneling magnetoresistance sensing circuit, the bandgap reference circuit further includes a first operational amplifier filter circuit and a second operational amplifier filter circuit; the first input terminal of the operational amplifier is connected to the drain of the first transistor through the first operational amplifier filter circuit, the second input terminal is connected to the drain of the second transistor through the first operational amplifier filter circuit, and the output terminal is connected to the gate of the first transistor through the second operational amplifier filter circuit.

[0010] Optionally, in the tunneling magnetoresistance sensing circuit, the resistance values of the second resistor, the fourth resistor, and the fifth resistor are adjustable.

[0011] Optionally, in the tunneling magnetoresistance sensing circuit, the second resistor, the fourth resistor, and the fifth resistor are register-controlled programmable resistors.

[0012] Optionally, in the tunneling magnetoresistance sensing circuit, adjust the resistance ratios among the first resistor, the second resistor, the third resistor, the fourth resistor, and the fifth resistor to change the magnitude and temperature coefficient of the reference voltage output by the bandgap reference circuit.

[0013] Optionally, in the tunneling magnetoresistance sensing circuit, the low temperature coefficient of the MOS transistor is in its saturation region.

[0014] Optionally, in the tunneling magnetoresistance sensing circuit, the source of the MOS transistor outputs a bias current at the level of 100 μA.

[0015] The tunneling magnetoresistance sensing circuit provided by the present invention includes a bandgap reference circuit, an operational transconductance amplifier, a MOS transistor, and a tunneling magnetoresistance sensor; the bandgap reference circuit is used to provide a reference voltage; the first input terminal of the operational transconductance amplifier is connected to the reference voltage, the second input terminal is connected to the source of the MOS transistor, and the output terminal is connected to the gate of the MOS transistor to perform negative feedback on the bias current output by the source of the MOS transistor; the drain of the MOS transistor is connected to the power supply voltage, and the source is connected to the tunneling magnetoresistance sensor to provide a bias current for the tunneling magnetoresistance sensor; by changing the reference voltage, the temperature coefficient of the bias current is changed. A bias current with a certain temperature coefficient is provided through the bandgap reference circuit, the operational transconductance amplifier, and the MOS transistor to compensate the sensitivity temperature coefficient of the tunneling magnetoresistance sensor, so that the tunneling magnetoresistance sensor is not easily affected by temperature to generate measurement deviation, and thus can be preferably applied to application scenarios with a wide operating temperature range and high-precision requirements, solving the problem that the existing tunneling magnetoresistance sensor is easily affected by temperature to generate measurement deviation. Description of the Drawings

[0016] Figure 1 is a schematic circuit diagram of the tunneling magnetoresistance sensing circuit provided in this embodiment; Figure 2 is a schematic circuit diagram of the tunneling magnetoresistance sensing circuit with a chopping circuit provided in this embodiment; Figure 3 is a circuit schematic diagram of the bandgap reference circuit provided in this embodiment; Figure 4 is a circuit schematic diagram of the bandgap reference circuit with a filtering circuit provided in this embodiment; Figure 5 is a partial schematic diagram of the waveforms of the output voltages of the tunneling magnetoresistance sensing circuit provided in this embodiment and the existing tunneling magnetoresistance sensor at -40°C and 100°C. Detailed Embodiments

[0017] The tunneling magnetoresistive sensing circuit proposed by the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise scales, only for conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention. In addition, the structures shown in the accompanying drawings are often part of the actual structures. In particular, the accompanying drawings need to show different focuses and sometimes use different scales.

[0018] It should be noted that the "first", "second", etc. in the description, claims and drawings of the present invention are used to distinguish similar objects in order to describe the embodiments of the present invention, rather than to describe a specific order or sequence. It should be understood that such structures can be interchanged under appropriate circumstances. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0019] The sensitivity temperature coefficient of existing traditional tunneling magnetoresistive sensors is usually relatively high, so that it is easy to generate measurement deviations in scenarios where the ambient temperature changes greatly, affecting the operation of the system. To solve this problem, a bias current with a certain temperature coefficient can be considered to compensate the sensitivity temperature coefficient of the tunneling magnetoresistive sensor. This bias current is usually generated by passing a voltage with a certain temperature coefficient through a resistor with zero temperature coefficient.

[0020] Currently, resistors with positive temperature coefficients and negative temperature coefficients are usually connected in series to obtain a resistor with zero temperature coefficient. In practical applications, not only the bandgap reference circuit (BGR) needs to be adjusted to generate an appropriate voltage, but also the control word of the resistor needs to be adjusted to obtain a resistor with zero temperature coefficient. However, the entire debugging process is difficult to characterize by simple electrical signals, so the debugging difficulty is relatively large.

[0021] Based on this, this embodiment provides a tunneling magnetoresistive sensing circuit, as Figure 1 shown, including a bandgap reference circuit BGR, an operational transconductance amplifier OTA, a MOS transistor M0, and a tunneling magnetoresistive sensor TMR; the bandgap reference circuit BGR is used to provide a reference voltage V REF ; the first input terminal of the operational transconductance amplifier OTA is connected to the reference voltage V REF, the second input terminal is connected to the source electrode of the MOS transistor M0, and the output terminal is connected to the gate electrode of the MOS transistor M0 to perform negative feedback on the bias current output from the source electrode of the MOS transistor M0; the drain electrode of the MOS transistor M0 is connected to the power supply voltage VCC, and the source electrode is connected to the tunneling magnetoresistive sensor TMR to provide a bias current for the tunneling magnetoresistive sensor TMR; by changing the reference voltage V REF , so as to change the temperature coefficient of the bias current.

[0022] The tunneling magnetoresistive sensing circuit provided in this embodiment provides a bias current with a certain temperature coefficient through a bandgap reference circuit, an operational transconductance amplifier, and a MOS transistor, compensates the sensitivity temperature coefficient of the tunneling magnetoresistive sensor, so that the tunneling magnetoresistive sensor is not easily affected by temperature and generates measurement deviation, and thus can be better applied to application scenarios with a wide operating temperature range and high-precision requirements, solving the problem that the existing tunneling magnetoresistive sensor is easily affected by temperature and generates measurement deviation.

[0023] In addition, the sensitivity temperature coefficient of the tunneling magnetoresistive sensor comes from , when the temperature coefficient of the reference voltage V REF is opposite to the sensitivity temperature coefficient of the tunneling magnetoresistive sensor, its temperature coefficient can be compensated. During the debugging process, for the tunneling magnetoresistive sensing circuit provided in this embodiment, only the bandgap reference circuit needs to be debugged. By changing the magnitude and temperature coefficient of the reference voltage output by it, the magnitude and temperature coefficient of the bias current supplied to the tunneling magnetoresistive sensor can be changed, reducing the debugging difficulty.

[0024] Actually, in the tunneling magnetoresistive sensing circuit provided in this embodiment, the bandgap reference circuit BGR, the operational transconductance amplifier OTA, and the MOS transistor M0 constitute a low-dropout regulator LDO with an adjustable temperature coefficient. In order to offset the sensitivity temperature coefficient of the tunneling magnetoresistive sensor TMR, if the tunneling magnetoresistive sensor TMR is a PTC structure, the low-dropout regulator LDO needs to be designed as an NTC structure correspondingly. For example, in this embodiment, when the tunneling magnetoresistive sensor TMR is a PTC structure, the MOS transistor M0 used is an NMOS.

[0025] Preferably, in order to reduce the noise in the tunneling magnetoresistive sensing circuit, in this embodiment, as Figure 2 shown, the tunneling magnetoresistive sensing circuit further includes a chopper circuit L0; the chopper circuit L0 is arranged before the first input terminal and the second input terminal of the operational transconductance amplifier OTA to reduce the noise of the reference voltage V REF input to the first input terminal and the bias current input to the second input terminal. The specific circuit structure of the chopper circuit is well known to those skilled in the art, and this application will not elaborate on it.

[0026] In practical applications, to ensure the ability to provide a bias current, the size of MOS transistor M0 is usually large. Generally, the source of MOS transistor M0 outputs a bias current in the order of 100 μA. Also, in practical applications, MOS transistor M0 preferably uses a MOS transistor with a low temperature coefficient and operates in its saturation region.

[0027] Further, in this embodiment, as Figure 3 shown, the bandgap reference circuit includes a first transistor M1, a second transistor M2, a third transistor M3, a fourth transistor M4, an operational amplifier OA, a first triode Q1, a second triode Q2, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and a fifth resistor R5.

[0028] Specifically, the sources of the first transistor M1, the second transistor M2, the third transistor M3, and the fourth transistor M4 are connected to the power supply voltage VCC, and their gates are connected together; the drain of the first transistor M1 is connected to the first input terminal of the operational amplifier OA, the first end of the first resistor R1, and the emitter of the first triode Q1; the drain of the second transistor M2 is connected to the second input terminal of the operational amplifier OA, the first end of the second resistor R2, and the first end of the third resistor R3; the drain of the third transistor M3 is connected to the first end of the fourth resistor R4; the drain of the fourth transistor M4 is connected to the first end of the fifth resistor R5, and the output terminal of the reference voltage V REF is led out; the output terminal of the operational amplifier OA is connected to the gate of the first transistor M1; the second end of the first resistor R1 is connected to an equipotential; the base and collector of the first triode Q1 are short - circuited and connected to an equipotential; the second end of the second resistor R2 is connected to the emitter of the second triode Q2; the base and collector of the second triode Q2 are short - circuited and connected to an equipotential; the second ends of the third resistor R3, the fourth resistor R4, and the fifth resistor R5 are all connected to an equipotential.

[0029] To enable the bandgap reference circuit BGR to compensate the sensitivity temperature coefficient of the tunneling magnetoresistive sensor TMR at any operating ambient temperature, in practical applications, the resistances of the second resistor R2, the fourth resistor R4, and the fifth resistor R5 can be made adjustable. Specifically, the second resistor R2, the fourth resistor R4, and the fifth resistor R5 can be programmable resistors controlled by a register.

[0030] In this way, the resistor with zero temperature coefficient formed by connecting two original resistors in series is integrated into the bandgap reference circuit BGR. Therefore, by only adjusting the resistance ratios among the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, and the fifth resistor R5 in the bandgap reference circuit BGR, the magnitude and temperature coefficient of the reference voltage V output by the bandgap reference circuit BGR can be changed, thereby reducing the debugging difficulty. REF

[0031] In practical applications, the first transistor M1, the second transistor M2, the third transistor M3, and the fourth transistor M4 are all PMOS transistors, and the first triode Q1 and the second triode Q2 are both PNP-type triodes, so that the bandgap reference circuit BGR has a PTC structure and is suitable for compensating the sensitivity temperature coefficient of the tunneling magnetoresistive sensor TMR with an NTC structure.

[0032] Preferably, in order to improve the accuracy of the reference voltage V generated by the bandgap reference circuit BGR REF in this embodiment, as Figure 4 shown, the bandgap reference circuit further includes a first filter circuit L1 and a second filter circuit L2; the drain of the first transistor M1 is connected to the first input terminal of the operational amplifier OA, the first end of the first resistor R1, and the emitter of the first triode Q1 through the first filter circuit L1; the drain of the second transistor M2 is connected to the second input terminal of the operational amplifier OA, the first end of the second resistor R2, and the first end of the third resistor R3 through the first filter circuit L1; the drain of the third transistor M3 is connected to the first end of the fourth resistor R4 through the second filter circuit L2; the drain of the fourth transistor M4 is connected to the first end of the fifth resistor R5 through the second filter circuit L2.

[0033] In practical applications, the first filter circuit L1 and the second filter circuit L2 can be chopper circuits, and their specific circuit structures are well known to those skilled in the art, and will not be elaborated in this application. Through the first filter circuit L1 and the second filter circuit L2, the current and voltage output from the drains of the first transistor M1, the second transistor M2, the third transistor M3, and the fourth transistor M4 can be filtered, thereby reducing the noise in the electrical signal and improving the signal accuracy.

[0034] More preferably, as Figure 4As shown, the bandgap reference circuit further includes a first operational amplifier filtering circuit L3 and a second operational amplifier filtering circuit L4; a first input terminal of the operational amplifier OA is connected to a drain of the first transistor M1 through the first operational amplifier filtering circuit L3, a second input terminal is connected to a drain of the second transistor M2 through the first operational amplifier filtering circuit L3, and an output terminal is connected to a gate of the first transistor M1 through the second operational amplifier filtering circuit L4.

[0035] In practical applications, the first operational amplifier filtering circuit L3 and the second operational amplifier filtering circuit L4 can also be chopper circuits, and their specific circuit structures are well known to those skilled in the art, and will not be elaborated in this application. Through the first operational amplifier filtering circuit L3 and the second operational amplifier filtering circuit L4, the current and voltage input and output by the operational amplifier OA can be filtered, thereby reducing the noise in the electrical signal and improving the signal accuracy.

[0036] Hereinafter, a specific embodiment is used to illustrate the advantages of the tunneling magnetoresistive sensing circuit provided by this application in terms of the sensitivity temperature coefficient compared with the existing tunneling magnetoresistive sensors.

[0037] In the tunneling magnetoresistive sensing circuit provided in this embodiment, the sensitivity temperature coefficient of the tunneling magnetoresistive sensor TMR is -630 ppm / °C to -1160 ppm / °C; the number of control word bits of the programmable resistor controlled by the register in the bandgap reference circuit BGR is 4 bits. Theoretically, the temperature coefficient adjustment accuracy of this tunneling magnetoresistive sensing circuit is about 40 ppm / °C.

[0038] As Figure 5 shown, in the existing tunneling magnetoresistive sensor, the difference in the output voltage values at extremely cold (-40 °C) and extremely hot (100 °C) ambient temperatures is 0.146 mV; while in the tunneling magnetoresistive sensing circuit provided in this embodiment, the difference in the output voltage values of the tunneling magnetoresistive sensor at extremely cold (-40 °C) and extremely hot (100 °C) ambient temperatures is 0.0086 mV. Compared with the existing tunneling magnetoresistive sensor, the sensitivity temperature coefficient of the tunneling magnetoresistive sensing circuit provided in this embodiment has decreased by about 17 times, and the temperature coefficient adjustment accuracy is 54.6 ppm / °C.

[0039] It can be seen that the tunneling magnetoresistance sensing circuit provided in this embodiment constructs a low-dropout regulator (LDO) with a certain temperature coefficient through a bandgap reference circuit, an operational transconductance amplifier, and MOS transistors to provide a bias current, compensating the sensitivity temperature coefficient of the tunneling magnetoresistance sensor, so that the tunneling magnetoresistance sensor is not easily affected by temperature and generates measurement deviation, and thus can be better applied to application scenarios with a wide operating temperature range and high-precision requirements. At the same time, during the debugging process, for the tunneling magnetoresistance sensing circuit provided in this embodiment, only the resistors in the bandgap reference circuit need to be debugged. By changing the magnitude and temperature coefficient of the reference voltage output by it, the magnitude and temperature coefficient of the bias current supplied to the tunneling magnetoresistance sensor can be changed, reducing the debugging difficulty.

[0040] It should be noted that the various embodiments in this specification are described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the various embodiments can be referred to each other. In addition, the different parts among the various embodiments can also be combined and used, and the present invention does not limit this.

[0041] The tunneling magnetoresistance sensing circuit provided in this embodiment includes a bandgap reference circuit, an operational transconductance amplifier, MOS transistors, and a tunneling magnetoresistance sensor. The bandgap reference circuit is used to provide a reference voltage. The first input terminal of the operational transconductance amplifier is connected to the reference voltage, the second input terminal is connected to the source electrode of the MOS transistor, and the output terminal is connected to the gate electrode of the MOS transistor to perform negative feedback on the bias current output from the source electrode of the MOS transistor. The drain electrode of the MOS transistor is connected to the power supply voltage, and the source electrode is connected to the tunneling magnetoresistance sensor to provide a bias current for the tunneling magnetoresistance sensor. By changing the reference voltage, the temperature coefficient of the bias current is changed. A bias current with a certain temperature coefficient is provided through the bandgap reference circuit, the operational transconductance amplifier, and the MOS transistors to compensate the sensitivity temperature coefficient of the tunneling magnetoresistance sensor, so that the tunneling magnetoresistance sensor is not easily affected by temperature and generates measurement deviation, and thus can be better applied to application scenarios with a wide operating temperature range and high-precision requirements, solving the problem that the existing tunneling magnetoresistance sensor is easily affected by temperature and generates measurement deviation.

[0042] The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention in any way. Any changes and modifications made by those of ordinary skill in the art of the present invention based on the above disclosure are within the scope of protection of the claims.

Claims

1. A tunneling magnetoresistance sensing circuit, characterized in that: The invention comprises a bandgap reference circuit, an operational transconductance amplifier, a MOS tube and a tunneling magnetoresistive sensor; the bandgap reference circuit is used to provide a reference voltage; the first input terminal of the operational transconductance amplifier is connected to the reference voltage, the second input terminal is connected to the source of the MOS tube, and the output terminal is connected to the gate of the MOS tube to perform negative feedback on the bias current output by the source of the MOS tube; the drain of the MOS tube is connected to the power supply voltage, and the source is connected to the tunneling magnetoresistive sensor to provide a bias current for the tunneling magnetoresistive sensor; the temperature coefficient of the bias current is changed by changing the reference voltage.

2. The tunneling magnetoresistance sensing circuit according to claim 1, characterized in that: The tunneling magnetoresistive sensing circuit also includes a chopper circuit; the chopper circuit is arranged before the first input terminal and the second input terminal of the operational transconductance amplifier to reduce noise of the reference voltage input to the first input terminal and the bias current input to the second input terminal.

3. The tunneling magnetoresistance sensing circuit according to claim 1, characterized in that: The bandgap reference circuit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, an operational amplifier, a first triode, a second triode, a first resistor, a second resistor, a third resistor, a fourth resistor, and a fifth resistor; The sources of the first transistor, the second transistor, the third transistor and the fourth transistor are connected to the power supply voltage, and the gates are connected; the drain of the first transistor is connected to the first input terminal of the operational amplifier, the first end of the first resistor, and the emitter of the first triode; the drain of the second transistor is connected to the second input terminal of the operational amplifier, the first end of the second resistor, and the first end of the third resistor; the drain of the third transistor is connected to the first end of the fourth resistor; the drain of the fourth transistor is connected to the first end of the fifth resistor, and the output end of the reference voltage is led out; the output end of the operational amplifier is connected to the gate of the first transistor; the second end of the first resistor is connected to the equipotential; the base and collector of the first triode are short-circuited and connected to the equipotential; the second end of the second resistor is connected to the emitter of the second triode; the base and collector of the second triode are short-circuited and connected to the equipotential; the second end of the third resistor, the second end of the fourth resistor, and the second end of the fifth resistor are all connected to the equipotential.

4. The tunneling magnetoresistance sensing circuit according to claim 3, characterized in that: The bandgap reference circuit also includes a first filtering circuit and a second filtering circuit; the drain of the first transistor is connected to the first input terminal of the operational amplifier, the first end of the first resistor, and the emitter of the first transistor through the first filtering circuit; the drain of the second transistor is connected to the second input terminal of the operational amplifier, the first end of the second resistor, and the first end of the third resistor through the first filtering circuit; the drain of the third transistor is connected to the first end of the fourth resistor through the second filtering circuit; and the drain of the fourth transistor is connected to the first end of the fifth resistor through the second filtering circuit.

5. The tunneling magnetoresistance sensing circuit according to claim 3, characterized in that: The bandgap reference circuit also includes a first operational amplifier filter circuit and a second operational amplifier filter circuit; the first input end of the operational amplifier is connected to the drain of the first transistor through the first operational amplifier filter circuit, the second input end is connected to the drain of the second transistor through the first operational amplifier filter circuit, and the output end is connected to the gate of the first transistor through the second operational amplifier filter circuit.

6. The tunneling magnetoresistance sensing circuit according to claim 3, characterized in that: The resistance values ​​of the second resistor, the fourth resistor and the fifth resistor are adjustable.

7. The tunneling magnetoresistance sensing circuit according to claim 6, characterized in that: The second resistor, the fourth resistor and the fifth resistor are programmable resistors controlled by registers.

8. The tunneling magnetoresistance sensing circuit according to claim 3, characterized in that: The resistance ratio among the first resistor, the second resistor, the third resistor, the fourth resistor and the fifth resistor is adjusted to change the magnitude and the temperature coefficient of the reference voltage output by the bandgap reference circuit.

9. The tunneling magnetoresistance sensing circuit according to claim 1, characterized in that: The low temperature coefficient of the MOS tube is in its saturation region.

10. The tunneling magnetoresistance sensing circuit according to claim 1, characterized in that: The source of the MOS tube outputs a bias current of the order of 100 μA.

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