High-integration-level miniaturized TMR magnetic field sensor and use method thereof

Abstract

The invention discloses a high-integration-level miniaturized TMR magnetic field sensor and a use method thereof, relates to the technical field of electrical equipment measurement, and solves the problems that most existing TMR sensors in the prior art are discrete devices, the system integration level is low, and the noise immunity and the stability are not high in an electric power environment with high-frequency signals and strong electromagnetic interference. The TMR magneto-sensitive unit, the signal conditioning circuit and the analog / digital interface are highly integrated in the same package, and the size of the sensor is remarkably reduced while high sensitivity and broadband response are kept. Besides, by optimizing the magnetoelectric structure design and the signal chain topology, background noise and bias drift are reduced, the measurement precision is improved, and the method is particularly suitable for high-density layout, complex electromagnetic environments and high-bandwidth measurement scenes. According to the invention, a better current measurement solution is provided for novel power systems such as a smart power grid, a modular power electronic device and a distributed energy system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power equipment measurement, and in particular to a high-integration small TMR magnetic field sensor and a use method thereof. BACKGROUND

[0002] With the continuous expansion of the scale of the power system and the increasing degree of intelligence, real-time perception and accurate monitoring of the operating state of power equipment are required. As one of the important means of current detection in the power system, magnetic field sensors play a key role in the state detection and fault diagnosis of devices such as transformers, circuit breakers, busbars, and cables. Especially in smart grid, renewable energy grid connection, DC power transmission, and rail transit power supply system application scenarios, high sensitivity, high precision, miniaturization, and integration are required for magnetic field / current measurement devices.

[0003] Traditional current measurement methods, such as transformers and shunts, have good stability in certain working conditions, but their large size, high power consumption, difficulty in achieving electrical isolation, and limited anti-interference ability have made it difficult to meet the growing miniaturization and intelligence requirements in modern power equipment. In recent years, magnetic field sensors based on the Hall effect have been widely used in current detection, with the advantages of non-contact measurement, simple structure, and low cost. However, Hall sensors still have obvious shortcomings in sensitivity, temperature drift characteristics, linearity, and noise performance, limiting their application in high-precision power measurement scenarios. Tunnel Magnetoresistance (TMR) technology, as a new type of magnetic field sensing technology that has developed rapidly in recent years, has extremely high sensitivity, excellent linearity, good temperature stability, and low power consumption characteristics, attracting more and more researchers and the industry. TMR sensors have high intrinsic signal-to-noise ratio and small packaging capacity, making it possible to realize high-integration, small size, and high-performance current / magnetic field detection devices. Although some TMR-based sensor products have been introduced, there are still many challenges in power equipment measurement applications: existing TMR sensors are mostly discrete devices that need to be used with external analog circuits such as amplification and filtering, which has low system integration and is not conducive to compact installation; the packaging size of some products is still large, making it difficult to adapt to space-limited high-voltage or high-density wiring applications; in addition, in high-frequency signal and strong electromagnetic interference power environments, how to achieve low-noise and high-stability measurement is still a technical bottleneck.

[0004] Therefore, there is a need for a high-integration small TMR magnetic field sensor and a use method thereof. SUMMARY

[0005] In view of the problems in the prior art that existing TMR sensors are mostly discrete devices, need to be used in combination with external analog circuits such as amplification and filtering, the system has low integration degree, and the noise resistance and stability are not high in a high-frequency signal and a strong electromagnetic interference power environment, the application provides a high-integration small TMR magnetic field sensor and a use method thereof, which can highly integrate a TMR magnetic sensitive unit, a signal conditioning circuit and an analog / digital interface in the same package, while maintaining high sensitivity and wide frequency band response, significantly reduces the sensor size, and improves the system anti-interference ability and reliability. By optimizing the magnetic-electric structure design and the signal chain topology, the background noise and the bias drift are reduced, the measurement accuracy is improved, and the application is particularly suitable for high-density layout, a complex electromagnetic environment and a high-bandwidth measurement scene. The specific technical scheme is as follows. A high-integration small TMR magnetic field sensor, comprising a TMR magnetic sensitive resistance chip, an integrated analog front-end chip, an alternating excitation bridge type driving circuit and an MCU, wherein: The TMR magnetic sensitive resistance chip comprises a Wheatstone bridge composed of four symmetrical magnetic sensitive resistance units, the resistance value of the magnetic sensitive resistance unit changes linearly with the size of an external vector magnetic field, and the change is converted into a differential voltage signal output through the bridge structure; The integrated analog front-end chip is used for converting the differential voltage output by the TMR magnetic sensitive resistance chip into a digital quantity; The MCU communicates with the AFE chip through SPI, sets the PGA amplification multiple, data acquisition rate, calibration function, chopping and alternating excitation function of the AFE, and reads the TMR chip output value converted by the AFE, and further transmits the sensing data to a PC or the like upper computer.

[0006] Preferably, the differential voltage output by the TMR magnetic sensitive resistance chip has a linear relationship with the external magnetic field, as shown in the following formula: Wherein 、 are two pairs of magnetic sensitive resistance units with approximately equal size and magnetic resistivity and opposite sensitive axis directions, is a chip sensitivity, is a vector magnetic field along the sensitive axis direction of the chip, is a zero point offset caused by 、 incomplete symmetry.

[0007] Preferably, the differential voltage output by the TMR magnetic sensitive resistance chip is represented as follows: Wherein is a bridge reference voltage.

[0008] Preferably, the differential signal is collected and converted by selecting an integrated analog front-end chip AD7195 to convert the differential voltage output by the TMR magnetic sensitive resistance chip into a digital quantity.

[0009] Preferably, the integrated analog front-end chip is integrated with a programmable amplifier, a 24-bit delta-sigma ADC, a calibration register, a chopping and an alternating excitation.

[0010] A use method of a high-integration miniaturized TMR magnetic field sensor, applied to the high-integration miniaturized TMR magnetic field sensor as described above, the use of alternating excitation and chopping functions can eliminate the influence of zero drift in the circuit, the alternating excitation is to reverse the polarity of the bridge reference voltage in the adjacent two sampling periods, the chopping is to average the sampling conversion results of the two periods, and the bridge reference voltages before and after the reversal are respectively denoted as and The process of eliminating the zero drift in the circuit is represented as follows: wherein and respectively represent the conversion encoding results of the previous period and the next period ADC, is the final encoding result after two-period averaging.

[0011] Preferably, the sensor is placed in a magnetic shielding box, the AD7195 system zero point calibration function is enabled, the zero magnetic field output is stored in the zero point register, and the inherent zero drift of the sensor chip is automatically subtracted in the subsequent conversion.

[0012] Preferably, the MCU with the model of STMWB55VGY6 is used to communicate with the AFE through the SPI interface, to set the PGA amplification multiple, data acquisition rate, calibration function, chopping and alternating excitation function of the AFE, and to read the TMR chip output value converted by the AFE, and further to transmit the sensor data to the PC and other upper computers through the serial port USART.

[0013] A computer readable storage medium, comprising a stored program, wherein the computer readable storage medium controls the device where the computer readable storage medium is located to execute the use method of the high-integration miniaturized TMR magnetic field sensor as described above when the program runs.

[0014] A processor for running a program, wherein the processor executes the use method of the high-integration miniaturized TMR magnetic field sensor as described above when the program runs.

[0015] Compared with the prior art, the beneficial effects of the present application are: The application integrates the TMR magnetic sensitive unit, the signal conditioning circuit and the analog / digital interface into the same package, significantly reduces the sensor size while maintaining high sensitivity and wide frequency band response, and improves the system anti-interference ability and reliability. In addition, the application optimizes the design of the magnetoelectric structure and the signal chain topology, reduces the noise floor and bias drift, and improves the measurement accuracy, especially suitable for high-density layout, complex electromagnetic environment and high-bandwidth measurement scenarios. Therefore, the application not only fills the gap of high-performance miniaturized magnetic field sensors in existing power equipment measurement, but also provides a better current measurement solution for smart grids, modular power electronic devices, distributed energy systems and other new power systems, and has wide application prospect and industrialization value. In summary, compared with the prior art, the application has at least the following four advantages: Compared with the prior art, the application has the following advantages: (1) The high-integration small TMR magnetic field sensor has a high-precision, low-noise integrated analog front end (AFE), which can realize high-precision acquisition and conversion of sensing signals; (2) The high-integration small TMR magnetic field sensor has an analog-digital conversion signal processing circuit with chopping and alternating excitation functions, and has low zero drift and low noise; (3) The high-integration small TMR magnetic field sensor has a zero point calibration function, which can further reduce the inherent zero point offset of the sensing system; (4) The high-integration small TMR magnetic field sensor selects high-integration chip packaging and high-density PCB design, and the PCB area is less than 2*2 cm2, which can be applied to compact magnetic field / current measurement scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the application, the drawings needed in the description of the specific embodiments or prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale.

[0017] Figure 1 is a schematic diagram of the overall structure of the application; Figure 2 is a schematic diagram of the programmable magnetoresistive current sensor circuit module structure; Figure 3 is a schematic diagram of the integrated analog front end module circuit; Figure 4 is a schematic diagram of the alternating excitation bridge drive module circuit; Figure 5 is a schematic diagram of the MCU module circuit; and Figure 6 This is the circuit schematic of the voltage regulator module; Figure 7 This is a schematic diagram of the sensor PCB layout; Figure 8 This is a schematic diagram of the sensor noise test results. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0020] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0021] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0022] like Figure 1 As shown, the sensor includes a TMR magnetoresistive chip, an integrated analog front-end (AFE) chip, an AC excitation bridge drive circuit, and an MCU (the MCU part is not shown in the figure). The TMR magnetoresistive chip has a bridge structure, consisting of four pairwise symmetrical magnetoresistive units, and its output differential voltage is linearly related to the external magnetic field, as shown in the following equation.

[0023] in , It consists of two pairs of magnetoresistive units that are approximately equal in size and magnetoresistivity, but whose sensitive axes are opposite in direction. For chip sensitivity, The vector magnetic field along the sensitive axis of the chip. Because of , Zero point shift due to incomplete symmetry.

[0024] The differential voltage output by the TMR chip can be expressed as: where is the bridge reference voltage.

[0025] To collect and convert the differential signal, an integrated analog front end (AFE) chip AD7195 is selected. The chip integrates a programmable amplifier (PGA) and a 24-bit delta-sigma ADC, which can convert the differential voltage output by the TMR magnetic sensitive resistance chip into a digital quantity, facilitating further transmission, processing and storage.

[0026] Due to the parasitic thermocouple effect of the amplifier input bias current through the loop resistance contact points of different metal materials such as pads and IC pins, the charge injection of the sampling capacitor when the ADC sampling switch is closed, and the electromagnetic interference coupling, there is a zero drift in the signal processing circuit, and the offset voltage may change with temperature, working environment and circuit state. It is embodied in Figure 1 , and .

[0027] To eliminate the influence of zero drift in the circuit, AC excitation and chopping functions can be enabled. AC excitation means reversing the polarity of the bridge reference voltage in the adjacent two sampling periods, and chopping means averaging the sampling and conversion results of the two periods. The bridge reference voltages before and after the reversal are denoted as and , respectively. The process can be expressed as: where and represent the conversion encoding results of the previous and next periods of ADC, respectively, is the final encoding result after averaging the two periods. As can be seen from the above formula, the zero drift in the circuit has been eliminated.

[0028] Based on the same principle, the low-frequency noise in the circuit can also be improved.

[0029] To further eliminate the inherent zero drift of the sensor chip , the AD7195 system zero point calibration function is enabled. The sensor is placed in a magnetic shielding box, and the chip automatically stores the zero magnetic field output into the zero point register, which is automatically subtracted in the subsequent conversion, realizing zero drift elimination.

[0030] In order to read the conversion results of the sensing signals and further process the transmission, the MCU with the model of STMWB55VGY6 is used to communicate with the AFE through the SPI interface, the PGA amplification multiple, data acquisition rate, calibration function, chopping and AC excitation function of the AFE are set, and the output values of the TMR chip of the AFE conversion are read, and the sensing data is further transmitted to the PC and the like upper computer through the serial port USART.

[0031] The sensor principle diagram is shown as Figures 2-6 Figure 2 The TMR magnetic sensitive resistance chip module, Figure 3 The integrated analog front-end module, Figure 4 The AC excitation bridge driving module, Figure 5 The MCU module, Figure 6 The voltage stabilizing module.

[0032] The sensor PCB layout is shown as Figure 7 The PCB layout is as compact as possible, and the above-mentioned circuit arrangement is realized on the PCB board with 19.8*19.3 mm2.

[0033] The sensor noise test is shown as Figure 8 The measured sensor RMS noise is 3.547 uVrms, the selected TMR chip sensitivity is 6 mV / V / Gs, so the sensor RMS noise is about 12 nTrms, the 1 / f noise is less than 4 nT / √Hz @ 1Hz, and the low noise and low zero drift measurement of the magnetic field is realized.

[0034] In summary, the TMR magnetic sensitive unit, the signal conditioning circuit and the analog / digital interface are highly integrated in the same package, the sensor size is significantly reduced while the high sensitivity and wide frequency band response are maintained, and the system anti-interference ability and reliability are improved. In addition, the background noise and bias drift are reduced, the measurement accuracy is improved, and the application is particularly suitable for high-density layout, complex electromagnetic environment and high-bandwidth measurement scene by optimizing the magnetic-electric structure design and signal chain topology. Therefore, the application not only fills the vacancy of high-performance small-sized magnetic field sensor in the existing power equipment measurement, but also provides a better current measurement solution for intelligent power grid, modular power electronic device, distributed energy system and other new power systems, and has wide application prospect and industrialization value.

[0035] ​Those skilled in the art can understand that the units of the examples described in combination with the embodiments disclosed herein can be realized in electronic hardware, computer software or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the components of the examples have been described in general terms in the above description. Whether the functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. The skilled person can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0036] In the embodiments provided by the present application, it should be understood that the division of units is only a logical functional division, and there can be another division manner in actual implementation, for example, multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored, etc.

[0037] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional unit.

[0038] When the integrated unit is realized in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application essentially or the part that contributes to the prior art or the whole or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a number of instructions for causing a computer device (which can be a personal computer, a server or a network device, etc.) to execute all or part of the steps of the methods described in the embodiments of the present application. The aforementioned storage medium includes: a U disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a mobile hard disk, a magnetic disk or an optical disk, and various media that can store program codes.

[0039] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the description of the present application.

Claims

1. A high-integration miniaturized TMR magnetic field sensor, characterized in that, The TMR magnetic sensitive resistance chip, the integrated analog front-end chip, the AC excitation bridge driving circuit and the MCU are included, wherein: The TMR magnetic sensitive resistance chip comprises a Wheatstone bridge composed of four symmetrical magnetic sensitive resistance units, the resistance value of the magnetic sensitive resistance unit linearly changes with the size of the external vector magnetic field, and the change is converted into a differential voltage signal output through the bridge structure; The integrated analog front-end chip is used for converting the differential voltage output by the TMR magnetic sensitive resistance chip into a digital quantity; The MCU communicates with the AFE chip through SPI, sets the PGA amplification multiple, data acquisition rate, calibration function, chopping and AC excitation function of the AFE, and reads the TMR chip output value converted by the AFE, and further transmits the sensing data to a PC or the like upper computer.

2. The high-integration and small-size TMR magnetic field sensor according to claim 1, characterized in that, The differential voltage output by the TMR magnetic sensitive resistance chip has a linear relationship with the external magnetic field, as shown in the following formula: wherein , are two pairs of magnetically sensitive resistance units having approximately equal size and magneto-resistivity, and opposite directions of the sensitive axis, is the sensitivity of the chip, is the vector magnetic field along the direction of the sensitive axis of the chip, is the zero point offset due to , the incomplete symmetry.

3. The high-integration and small-size TMR magnetic field sensor according to claim 2, characterized in that, The differential voltage output by the TMR magnetic sensitive resistance chip is represented as follows: wherein is a bridge reference voltage.

4. The high-integration and small-size TMR magnetic field sensor according to claim 1, characterized in that, The differential signal is collected and converted, the integrated analog front-end chip AD7195 is selected, and the differential voltage output by the TMR magnetic sensitive resistance chip is converted into a digital quantity.

5. The high-integration and small-size TMR magnetic field sensor according to claim 1, characterized in that, The integrated analog front-end chip integrates a programmable amplifier, a 24bit delta-sigma ADC, a calibration register, chopping and AC excitation.

6. A method of using a high-integration miniaturized TMR magnetic field sensor, applied to a high-integration miniaturized TMR magnetic field sensor according to any one of claims 1-5, characterized in that, The function of AC excitation and chopping can eliminate the influence of zero drift in the circuit. The AC excitation means that the polarity of the bridge reference voltage is reversed in the adjacent two sampling periods, and the chopping means that the sampling conversion results of the two periods are averaged. The bridge reference voltages before and after the reversal are respectively denoted as and The process of eliminating the zero drift in the circuit is shown as follows: wherein and respectively represent the conversion encoding results of the previous cycle and the next cycle ADC, is the final encoding result after two-cycle averaging.

7. The method of using a highly integrated miniaturized TMR magnetic field sensor according to claim 6, characterized in that, The sensor is placed in a magnetic shielding box, the AD7195 system zero point calibration function is enabled, the zero magnetic field output is stored in the zero point register, and the inherent zero drift of the sensor chip is automatically subtracted in the subsequent conversion.

8. The method of using a highly integrated miniaturized TMR magnetic field sensor according to claim 6, characterized in that, The MCU with the model of STMWB55VGY6 communicates with the AFE through the SPI interface, sets the PGA amplification multiple, data acquisition rate, calibration function, chopping and AC excitation function of the AFE, reads the TMR chip output value converted by the AFE, and further transmits the sensing data to a PC or the like upper computer through the serial port USART.

9. A computer-readable storage medium, characterized in that, The computer readable storage medium comprises a stored program, wherein when the program runs, the device where the computer readable storage medium is located is controlled to execute the use method of the high-integration small-size TMR magnetic field sensor in any one of claims 6 to 8.

10. A processor, comprising: The processor is used for running a program, wherein the program runs to execute the use method of the high-integration small-size TMR magnetic field sensor in any one of claims 6 to 8.

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