Magnetic field sensor

Abstract

The invention provides a magnetic field sensor. The magnetic field sensor adopts an operational amplifier circuit with a magnetic resistor and an amplifier as a circuit form; the magnetic resistor is located in a feedback network which feeds back signals of the output end of the amplifier to the input end of the amplifier, so that the signals of the output end of the amplifier are modulation signals based on resistance value changes of the magnetic resistor. When the feedback can be positive feedback, the modulation signal is a frequency modulation signal, and when the feedback is negative feedback, the modulation signal is an amplitude modulation signal. The magnetic field sensor provided by the invention is convenient for extracting an effective signal from a direct-current component (noise) when a weak magnetic field is measured, and is simple in structure and easy to realize by adopting a semiconductor process.

Description

Technical Field

[0001] The present application relates to the field of magnetic field measurement, or the design and manufacture of magnetic sensors, and in particular to a magnetic field sensor suitable for measuring and extracting weak magnetic field signals. Background Art

[0002] Magnetic field sensors are divided into magnetic field sensors and vector magnetic field sensors according to the magnetic field information that can be measured. Magnetic field sensors only measure the intensity of the magnetic field and are not directly sensitive to the direction of the magnetic field (i.e., they do not provide information about the direction of the magnetic field). This type of sensor is widely used in geophysical exploration, navigation systems, biomedical imaging, and security testing. At present, magnetic field sensor technology has made significant progress, mainly including the following types and technical features: 1. Atomic Magnetometers: They use the interaction between the electron or nuclear spin inside an atom and the external magnetic field to measure the magnetic field strength. They have extremely high sensitivity and resolution, which can reach the femtotesla (fT) level. In recent years, optically pumped magnetometers based on rubidium vapor chambers have developed rapidly. They use lasers to excite rubidium atoms to achieve high-precision measurements of the Earth's magnetic field and even weak biological magnetic fields.

[0003] 2. Superconducting Quantum Interference Devices (SQUIDs): It is an extremely sensitive magnetic flux detector that can sense very small changes. SQUID can be used not only for field strength measurement, but also for gradient measurement, and it performs particularly well in the low frequency band. However, due to the need to work in a low temperature environment, its application range is subject to certain restrictions.

[0004] 3. Zero-Field Nuclear Magnetic Resonance (ZF-NMR) technology: This is an emerging method that can operate under conditions close to zero external magnetic field, thus avoiding the strong static magnetic field source required in traditional NMR methods. This method is particularly suitable for the design of portable devices and shows advantages in certain specific application scenarios.

[0005] 4. MEMS / Nano-electromechanical Systems (MEMS / NEMS) magnetic sensors: These miniaturized devices usually work based on the principles of anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR) effect or tunnel magnetoresistance (TMR). With the advancement of manufacturing technology, such sensors are moving towards smaller size, lower power consumption and higher integration.

[0006] 5. Diamond Nitrogen-Vacancy Centers (NV centers): NV defect centers in diamond exhibit excellent optical and magnetic properties and can be used as efficient single-spin probes to construct new magnetic field sensors. This technology combines optical readout, can operate at room temperature and pressure, and has good stability and anti-interference capabilities.

[0007] Among the above types, magnetic field sensors based on MEMS / micro-nano electromechanical systems (MEMS / NEMS) magnetic sensors are widely used in various electrical equipment or experimental environments due to their low cost and small size (realized by semiconductor technology). This type of magnetic sensor usually adopts a differential output mode of a bridge structure in order to eliminate common-mode interference signals; however, due to many restrictions such as process conditions and cost, it is difficult for each bridge arm to be completely consistent, resulting in differences in the static output of the two differentials, that is, the DC component (offset). The influence of the DC component is particularly obvious in low-frequency weak magnetic field measurement applications: in order to obtain weak magnetic signals, high-gain circuit design is usually used, resulting in saturation of the op amp output or a reduced detection dynamic range. Designers are often forced to use a power supply with a higher power amplitude, or add a multi-stage zeroing circuit; or both, but the new circuit will also introduce new interference. Based on the above reasons, it can be seen that existing magnetic field sensors are prone to failure when measuring weak signals. Summary of the invention

[0008] In view of the above-mentioned deficiencies of existing magnetic field sensors based on MEMS / micro-nano electromechanical systems (MEMS / NEMS) magnetic sensitive elements, the present application provides a magnetic field sensor that can measure weak magnetic field signals and is easy to extract effective signals. The magnetic field sensor is based on the feedback mechanism of an integrated operational amplifier, which modulates the low-frequency and weak magnetic signal to be measured onto a high-frequency fundamental wave, so that the output signal is an amplitude modulated signal or a frequency modulated signal based on the magnetic field strength. An AC (alternating current) coupling circuit or a bandpass circuit is used to suppress the DC component and amplify the weak magnetic signal with high gain; the amplified magnetic signal is then demodulated to obtain the low-frequency and weak magnetic field signal to be measured.

[0009] The circuit form of the magnetic field sensor provided by the present application is an operational amplifier circuit having a magnetic resistor and an amplifier. The magnetic resistor is located in the feedback network of the operational amplifier circuit, so that the output signal of the amplifier is a modulated signal based on the change of the resistance value of the magnetic resistor. The feedback network is used to feed back the output signal of the amplifier to its input. The feedback can be positive feedback or negative feedback.

[0010] When the circuit form of the magnetic field sensor is a closed-loop operational amplifier circuit with voltage negative feedback, the magnetic resistor is located in the negative feedback loop of the closed-loop operational amplifier circuit; and the output end signal is an amplitude modulated signal based on the resistance value change of the magnetic resistor.

[0011] Preferably, in the closed-loop operational amplifier circuit, the positive phase input terminal of the amplifier is connected to the modulated voltage signal Ve (i.e., Ve is a carrier signal with a certain frequency) through a resistor Rp, and its negative phase input terminal is connected to its output terminal through a magnetic resistor Rt, and is grounded through a series structure of a resistor Rn and a filter capacitor Cn.

[0012] When the circuit form of the magnetic field sensor is an oscillating circuit, the magnetic resistance is the resonant resistance of the oscillating circuit (located in a positive feedback network). The output end signal is a frequency modulated signal based on the change of the resistance value of the magnetic resistance.

[0013] In some embodiments, in the oscillation circuit (Wien bridge circuit), the positive phase input terminal of the amplifier is connected to the reference ground Vr through the parallel structure of capacitor C2 and magnetic resistor Rt1, and is connected to the output terminal of the amplifier through the series structure of capacitor C1 and magnetic resistor Rt2; the negative phase input terminal of the amplifier is connected to a negative feedback network arranged between the output terminal of the amplifier and the reference ground Vr. The negative feedback network is used to ensure the oscillation of the oscillation circuit and reduce the distortion (waveform deformation) of the oscillation signal. In this embodiment, the carrier signal is the intrinsic oscillation signal of the entire oscillation circuit in a zero magnetic environment, and there is no need to input the carrier signal from the outside, so the implementation method of the entire measurement system is more concise.

[0014] Preferably, the negative feedback network includes a series structure consisting of a resistor Rg and a resistor R1 connected between the output end of the amplifier and the reference ground Vr, and a series structure consisting of a resistor R2 and a bidirectional diode D connected in parallel at both ends of the resistor R1; the connection point of the resistor Rg and the resistor R1 is connected to the negative phase input end of the amplifier. Furthermore, the magnetoresistance is an XMR magnetoresistance element, and the XMR includes GMR, TMR, and AMR.

[0015] The magnetic field sensor provided by the present application utilizes the influence of the feedback mechanism of the operational amplifier circuit on the output information, and organically embeds the magnetic resistance into the signal feedback path of the operational amplifier circuit to realize the sensing output signal as a modulated signal based on the magnetic field strength. The magnetic field sensor provided by the present application has a simple structure, low manufacturing cost, is easy to implement using semiconductor technology (without inductance), and can effectively measure weak magnetic field signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 A circuit schematic diagram of a magnetic field sensor provided in the present application in one embodiment.

[0018] Figure 2 A circuit schematic diagram of another embodiment of the magnetic field sensor provided by the present application. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0021] The present application provides a magnetic field sensor, the circuit form of which is an operational amplifier circuit having a magnetic resistor and an amplifier. The magnetic resistor is located in a feedback network of the operational amplifier circuit, so that the output signal of the amplifier is a modulated signal based on the change in the resistance value of the magnetic resistor. The feedback network is used to feed back the output signal of the amplifier to its input. The feedback is not limited to negative feedback, but can also be positive feedback. exist Figure 1 In the illustrated embodiment, the circuit form of the magnetic field sensor provided by the present application is a closed-loop operational amplifier circuit with voltage negative feedback. The closed-loop operational amplifier circuit includes an amplifier A, a magnetic resistor Rt, resistors Rp, Rn, and a filter capacitor Cn. The positive input terminal of the amplifier A is connected to the modulated voltage signal Ve (carrier signal) through the resistor Rp, and its negative input terminal is connected to its output terminal through the magnetic resistor Rt, and is grounded through the series structure of the resistor Rn and the filter capacitor Cn.

[0022] From the circuit analysis, it can be seen that the output signal Vo of the amplifier A is: ; (1) The output signal Vo of amplifier A changes with the resistance value of magnetic resistor Rt, and the output signal Vo forms an amplitude modulation of the input signal Ve. That is, the magnetic field strength signal is modulated and amplified to the carrier Ve, forming an envelope signal of a certain frequency and outputting it. The subsequent receiving end can obtain the magnetic field strength information through the corresponding demodulation circuit.

[0023] exist Figure 2 In another embodiment shown, the circuit form of the magnetic field sensor provided by the present application is an oscillation circuit (Wien bridge circuit), and the magnetic resistance is the resonant resistance of the oscillation circuit (located in a positive feedback network).

[0024] like Figure 2 As shown, the oscillation circuit includes an amplifier A, magnetic resistors Rt1, Rt2, filter capacitors C1, C2, resistors Rg, R1, R2 and a bidirectional diode D. The positive phase input terminal of the amplifier A is connected to the reference ground Vr through a parallel structure of capacitor C2 and magnetic resistor Rt1, and is connected to the output terminal of the amplifier A through a series structure of capacitor C1 and magnetic resistor Rt2. The negative phase input terminal of the amplifier A is connected to a negative feedback network arranged between its output terminal and the reference ground Vr.

[0025] The negative feedback network includes a series structure consisting of a resistor Rg and a resistor R1 connected between the output end of the amplifier A and the reference ground Vr, and a series structure consisting of a resistor R2 and a bidirectional diode D connected in parallel at both ends of the resistor R1. The connection point of the resistor Rg and the resistor R1 is connected to the negative phase input end of the amplifier. The negative feedback network is used to ensure that the oscillation circuit starts oscillating and reduce the distortion (waveform deformation) of the oscillation signal.

[0026] From the circuit analysis, it can be known that the electrical connection of magnetic resistors Rt1, Rt2, filter capacitors C1, C2 and amplifier A constitutes a series-parallel oscillation circuit (Wien bridge circuit). , that is, the magnetic resistances Rt1 and Rt2 are the same, and the filter capacitors C1 and C2 are the same; since the magnetic resistances Rt1 and Rt2 replace the resonant resistors in the traditional Wien oscillation circuit, it can be seen that the frequency f of the output signal of amplifier A is: ;(2) It can be seen from the above formula (2) that the frequency f of the output signal of amplifier A changes with the resistance value R of the magnetic resistor Rt, and the output signal (i.e., the oscillation signal) is a frequency modulated signal based on the resistance value R of the magnetic resistor Rt; that is, the magnetic field strength signal is used to modulate the output signal frequency of the oscillation circuit. The subsequent receiving end can obtain the magnetic field strength information through the corresponding demodulation circuit (for example, access to a frequency counter). Resistors Rg, R1, R2 and bidirectional diode D constitute a negative feedback network, which is used to ensure the oscillation of the oscillation circuit and reduce the distortion (waveform deformation) of the oscillation signal.

[0027] Furthermore, the magnetoresistance is an XMR magnetoresistance element including GMR, TMR, and AMR.

[0028] The above description is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A magnetic field sensor, characterized in that: The circuit form of the magnetic field sensor is an operational amplifier circuit having a magnetic resistor and an amplifier; wherein the magnetic resistor is located in a feedback network of the operational amplifier circuit, so that the output signal of the amplifier is a modulated signal based on the change in the resistance value of the magnetic resistor; and the feedback network is used to feed back the output signal to the input of the amplifier.

2. The magnetic field sensor according to claim 1, characterized in that The circuit form of the magnetic field sensor is a closed-loop operational amplifier circuit with voltage negative feedback, and the magnetic resistor is located in the negative feedback loop of the closed-loop operational amplifier circuit; the output end signal is an amplitude modulated signal based on the resistance value change of the magnetic resistor.

3. The magnetic field sensor according to claim 1, characterized in that: The circuit form of the magnetic field sensor is an oscillation circuit, the magnetic resistance is the resonant resistance of the oscillation circuit; and the output end signal is a frequency modulation signal based on the change of the resistance value of the magnetic resistance.

4. The magnetic field sensor according to claim 2, characterized in that: In the closed-loop operational amplifier circuit, the positive input terminal of the amplifier is connected to the modulated voltage signal Ve through a resistor Rp, and the negative input terminal is connected to its output terminal through a magnetic resistor Rt and is grounded through a series structure of a resistor Rn and a filter capacitor Cn.

5. The magnetic field sensor according to claim 3, characterized in that: In the oscillation circuit, the positive phase input terminal of the amplifier is connected to the reference ground Vr through a parallel structure of a capacitor C2 and a magnetic resistor Rt1, and is connected to the output terminal of the amplifier through a series structure of a capacitor C1 and a magnetic resistor Rt2; the negative phase input terminal of the amplifier is connected to a negative feedback network arranged between its output terminal and the reference ground Vr.

6. The magnetic field sensor according to claim 5, characterized in that The feedback network includes a series structure consisting of a resistor Rg and a resistor R1 connected between the output end of the amplifier and the reference ground Vr, and a series structure consisting of a resistor R2 and a bidirectional diode D connected in parallel at both ends of the resistor R1; wherein the connection point of the resistor Rg and the resistor R1 is connected to the negative phase input end of the amplifier.

7. The magnetic field sensor according to any one of claims 1 to 6, characterized in that: The magnetoresistance is an XMR magnetoresistance element, and the XMR includes GMR, TMR, and AMR.

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