Digital fluxgate magnetometer system based on 1-bit sigma-delta digital-to-analog converter

Abstract

The invention belongs to the field of deep space exploration and space science, and relates to a digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter, which comprises a sensor probe for sensing the size and direction of an environment magnetic field by adopting a single-axis fluxgate sensor and outputting a magnetic field signal to an analog circuit module, receiving excitation current and feedback current to maintain the working state of the magnetic core; the analog circuit module generates excitation current, performs amplification and analog-to-digital conversion on the received magnetic field signal, performs digital-to-analog conversion, filtering and driving on the signal output by the digital circuit module, and outputs feedback current to a feedback coil of the sensor probe; and the digital circuit module is realized based on an FPGA, performs phase-sensitive demodulation, digital integration, 1-bit sigma-delta modulation, down-sampling and digital low-pass filtering on the digital signal after analog-to-digital conversion, outputs the processed magnetic field detection data to an upper computer, and generates a synchronous clock signal to the analog circuit module at the same time.

Description

Technical Field

[0001] This invention belongs to the field of deep space exploration and space science, and specifically relates to a digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter. Background Technology

[0002] The space magnetic field is a core fundamental physical quantity in space science research, playing an irreplaceable role in several key areas such as space weather monitoring, analysis of celestial body origins and evolution, and early warning of spacecraft orbital safety. Fluxgate magnetometers, due to their advantages of high precision, small size, and high reliability, have become commonly used detection instruments in the field of vector magnetic field measurement. However, traditional analog fluxgate magnetometers have limitations such as complex signal processing procedures, weak anti-interference capabilities, and poor long-term stability, making it difficult to meet the stringent requirements of high precision and high reliability for current deep space exploration missions.

[0003] Digital fluxgate magnetometers, with their high resolution, wide measurement range, and adaptability to harsh environments, are gradually becoming the development trend for space magnetic field detection. However, the performance of existing digital fluxgate magnetometers heavily relies on the accuracy of the digital-to-analog converter (DAC). Traditional DACs using Nyquist modulation technology suffer from insufficient linearity and weak high-frequency noise suppression. In complex space environments such as strong radiation and extreme temperatures, component characteristics are prone to drift, leading to decreased detection accuracy and shortened lifespan, failing to meet the core requirements of deep space exploration missions for long lifespan and high accuracy. Therefore, there is an urgent need for a digital fluxgate magnetometer system that incorporates 1-bit sigma-delta modulation and 1-bit digital-to-analog conversion in a closed-loop feedback loop to achieve noise shaping and reduce dependence on high-precision multi-bit DACs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter. It adopts 1-bit sigma-delta modulation technology to replace the traditional Nyquist modulation technology. By constructing a high-order single-loop modulator model and optimizing the signal processing flow, it effectively improves the linearity and resolution of the digital-to-analog conversion, reduces the impact of component characteristic drift on system performance, and ensures long-term stable operation of the system in harsh environments such as strong radiation and wide temperature range, thus providing more reliable technical support for space magnetic field detection.

[0005] In view of this, the present invention provides a digital fluxgate magnetometer system based on a 1-bit sigma-delta analog-to-digital converter, the system comprising: a sensor probe, an analog circuit module, and a digital circuit module; wherein, The sensor probe is a single-axis fluxgate sensor, which includes a magnetic core and an excitation coil, a signal coil and a feedback coil wound around the magnetic core. It is used to sense the magnitude and direction of the ambient magnetic field, output the measured magnetic field signal to the analog circuit module, and receive excitation current and feedback current to maintain the working state of the magnetic core. The analog circuit module is used to generate excitation current, amplify and convert the received magnetic field signal into an analog-to-digital signal, and also to convert, filter and drive the signal output by the digital circuit module into an analog-to-digital signal, and output feedback current to the feedback coil of the sensor probe. The digital circuit module, implemented on an FPGA, is used to process the digital signal after analog-to-digital conversion, including phase-sensitive demodulation, digital integration, 1-bit sigma-delta modulation, downsampling, and digital low-pass filtering. It outputs the processed magnetic field detection data to the host computer and simultaneously generates a synchronous clock signal to the analog circuit module.

[0006] As an improvement to the above system, the analog circuit module includes: an excitation module, a preamplifier, an AD converter, an analog low-pass filter, and a feedback drive module; wherein, The excitation module is used to receive the synchronous clock signal generated from the digital circuit module, generate an excitation current, and provide it to the excitation coil to generate a periodic excitation magnetic field signal. The preamplifier is used to connect to the signal coil and amplify the induced signal; The AD converter is used to convert the amplified induced signal into a digital signal and output it to the digital circuit module. The analog low-pass filter is used to filter out high-frequency modulation noise; The feedback drive module is used to provide feedback current to the feedback coil, ensuring that the magnetic core works in a zero magnetic state and completing the negative feedback operation.

[0007] As an improvement to the above system, the preamplifier is a low-power instrumentation amplifier, and a fixed gain is set for the signal output from the signal coil.

[0008] As an improvement to the above system, the feedback drive module uses a low-noise precision operational amplifier to drive the feedback coil to generate a compensation magnetic field opposite to the direction of the external magnetic field, ensuring that the magnetic core works in a zero-magnetic state.

[0009] As an improvement to the above system, the digital circuit module includes: a clock synchronization module, a phase-sensitive demodulation module, a digital integration module, a 1-bit sigma-delta modulation module, a downsampling module, a digital low-pass filter, and a data transmission module; wherein, The clock synchronization module is used to generate a synchronous clock signal to the excitation module, and also to generate a demodulated square wave signal to output to the phase-sensitive demodulation module; The phase-sensitive demodulation module is used to extract even-order harmonic components from the output signal of the AD converter and suppress high-frequency noise. The digital integration module is used to perform cumulative smoothing processing on the instantaneous signal output by the phase-sensitive demodulation module; The 1-bit sigma-delta modulation module is used to quantize the signal output by the digital integrator module into a 1-bit digital stream; The downsampling module is used to reduce the data rate of the signal output by the digital integration module; The digital low-pass filter module is used to filter out out-of-band high-frequency noise from the signal output by the downsampling module; The data transmission module is used to send the magnetic field detection data processed by the digital low-pass filter module to the host computer via a serial port.

[0010] As an improvement to the above system, the 1-bit sigma-delta modulation module adopts a high-order single-loop modulator structure and uses noise shaping technology to push quantization noise to the high-frequency band in order to improve the signal-to-noise ratio and linearity within the signal bandwidth.

[0011] As an improvement to the above system, the higher-order single-loop modulator is a fifth-order single-loop sigma-delta modulator.

[0012] As an improvement to the above system, the clock synchronization module generates two co-source clock signals, which are used for the excitation module and the phase-sensitive demodulation module respectively, to ensure the synchronization of excitation and demodulation.

[0013] As an improvement to the above system, the magnetic core is made of permalloy material to reduce hysteresis loss and improve magnetic field induction sensitivity.

[0014] Compared with the prior art, the advantages of the present invention are: This invention, based on the closed-loop feedback structure of a traditional digital fluxgate magnetometer, introduces 1-bit sigma-delta modulation and combines it with a 1-bit digital-to-analog converter to form a feedback drive loop. The excitation and demodulation reference are simultaneously constrained by a synchronous clock from the same source. This allows for meeting the closed-loop feedback measurement requirements while reducing the dependence on the linearity of a high-precision multi-bit DAC and device matching. Furthermore, noise shaping shifts quantization errors to higher frequencies, and filtering suppresses their in-band effects, thereby improving the system's stability and reliability in complex space environments such as high radiation and extreme temperatures. This meets the requirements of deep space exploration missions for long lifespan, high precision, and high reliability. Attached Figure Description

[0015] Figure 1This is a block diagram of the overall structure of the digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to the present invention. Figure 2 This is a flowchart of the signal processing of the digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to the present invention. Detailed Implementation

[0016] The purpose of this invention is to address the technical shortcomings of existing digital fluxgate magnetometers, which rely on traditional Nyquist modulation digital-to-analog converters (DACs). These DACs suffer from insufficient linearity, weak high-frequency noise suppression, and are prone to accuracy drift and shortened lifespan in complex space environments such as high radiation and extreme temperatures. This invention aims to provide a digital fluxgate magnetometer system based on a 1-bit sigma-delta DAC. By constructing a high-order single-loop 1-bit sigma-delta modulator model and optimizing the circuit architecture and signal processing flow, the accuracy bottleneck of traditional DACs is overcome, improving the system's adaptability to harsh environments. This achieves high-precision, high-reliability space magnetic field detection, meeting the requirements of deep space exploration, satellite magnetic field measurement, and space weather early warning missions for long-life, high-resolution magnetic field detection equipment.

[0017] To achieve the above-mentioned objectives, this invention provides a digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter (hereinafter referred to as the "1-bit digital magnetometer system"), such as... Figure 1 As shown, the system consists of three parts: a sensor probe, an analog circuit module, and a digital circuit module. The modules are connected through standardized interfaces to form a closed-loop collaborative working circuit.

[0018] 1. Sensor probe: The sensor probe is a single-axis fluxgate sensor probe, which senses the characteristic components of the external magnetic field. Its core magnetic core is made of permalloy material with high permeability and low coercivity to reduce hysteresis loss and improve magnetic field sensing sensitivity. The probe has three sets of coils: an excitation coil, a signal coil, and a feedback coil. The excitation coil receives the excitation current to generate a periodic saturation magnetic field; the signal coil converts changes in the external magnetic field into an electrical signal; and the feedback coil receives the feedback current to generate a compensation magnetic field, ensuring that the magnetic core operates in a zero-magnetic state.

[0019] 2. Analog circuit module: The analog circuit module implements signal conversion and driving functions, including an excitation module, a preamplifier, an AD converter, an analog low-pass filter, and a feedback drive module.

[0020] (1) The excitation module is used to receive the stable clock signal output by the digital circuit module and generate a periodic stable excitation current through the high-speed drive circuit to ensure that the excitation coil generates a periodic excitation magnetic field with stable frequency and uniform amplitude, so that the sensor core is alternately saturated.

[0021] (2) The preamplifier is a low-cost, low-power instrumentation amplifier with a fixed gain set for the signal output from the signal coil.

[0022] (3) The AD converter is connected to the digital circuit module to convert the analog signal output by the preamplifier into a digital signal, providing high-quality input for subsequent digital signal processing.

[0023] (4) The analog low-pass filter adopts a low-pass active filter to filter out high-frequency modulation noise in the 1-bit sigma-delta DAC output signal and output a high-precision analog feedback signal.

[0024] (5) The feedback drive module uses a low-noise precision operational amplifier to receive the feedback signal output by the analog low-pass filter and drive the feedback coil to generate a compensation magnetic field that is equal in magnitude and opposite in direction to the external magnetic field, so that the sensor core always works in a zero magnetic state, completes the negative feedback closed-loop control, and improves the linearity of the system.

[0025] 3. Digital circuit module The digital circuit module handles digital signal processing and synchronization control, implementing the core algorithm based on an FPGA. It includes a clock synchronization module, a phase-sensitive demodulation module, a digital integration module, a 1-bit sigma-delta modulation module, a downsampling module, a digital low-pass filter module, and a data transmission module. Specifically, the 1-bit digital signal output from the 1-bit sigma-delta modulation is converted into an analog feedback signal for driving the feedback coil by a 1-bit digital-to-analog converter. This achieves closed-loop feedback drive on the basis of a traditional digital fluxgate magnetometer structure and reduces the dependence on multi-bit digital-to-analog conversion.

[0026] (1) The clock synchronization module generates two synchronous clock signals by FPGA. The two clocks are designed from the same source to ensure the synchronization of the excitation signal and the demodulation signal and improve the noise suppression efficiency.

[0027] (2) The phase-sensitive demodulation module extracts the even harmonic components in the digital signal output by the AD converter through the multiplier, while suppressing the odd harmonics and high-frequency noise.

[0028] (3) The digital integration module uses an accumulation algorithm to process the instantaneous signal after phase-sensitive demodulation, eliminate the influence of random noise, and output stable magnetic field data.

[0029] (4) The 1-bit sigma-delta modulation module adopts a high-order single-loop modulator structure to quantize the multi-bit signal output by the digital integration module into a 1-bit digital signal; the quantization noise is pushed to the high-frequency band by noise shaping technology to move away from the signal bandwidth, thereby improving the signal-to-noise ratio and linearity within the signal bandwidth.

[0030] (5) The downsampling module reduces the high-speed 1-bit data stream (in accordance with the Nyquist sampling theorem).

[0031] (6) The digital low-pass filter module filters out out-of-band high-frequency noise, reducing the pressure on subsequent data transmission and processing.

[0032] (7) The data transmission module communicates via the serial port on the FPGA module, packages the magnetic field data after digital low-pass filtering according to a custom frame format. In one embodiment, the frame format is: frame header + data + check bit, and outputs it to the host computer.

[0033] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0034] Example 1 Embodiment 1 of this invention proposes a digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter. It is a high-precision, high-reliability space magnetic field detection system suitable for scenarios requiring high-precision magnetic field detection, such as deep space exploration, satellite magnetic field measurement, geomagnetic mapping, and space weather early warning.

[0035] The hardware selection and setup of this system includes three parts: sensor selection and installation, analog circuit module implementation, and digital circuit module implementation, as detailed below: The sensor probe is a single-axis fluxgate sensor probe. Its magnetic core is made of permalloy material with high permeability and low coercivity. It consists of three parts: excitation coil, signal coil, and feedback coil. The sensor probe is installed at the end of the spacecraft's extension rod to ensure that the distance between the probe and other electronic equipment can reduce electromagnetic interference.

[0036] The analog circuit module includes: excitation module, preamplifier, AD converter, analog low-pass filter, and feedback drive module.

[0037] Excitation module: Receives a stable clock signal from the digital circuit module and generates a periodic stable excitation current through a high-speed drive circuit. This ensures that the excitation coil generates a periodic excitation magnetic field with a stable frequency and uniform amplitude, causing the sensor core to saturate alternately.

[0038] Preamplifier: Amplifies analog signals.

[0039] AD converter: Communicates with digital circuit modules to ensure fast data transmission.

[0040] Analog low-pass filter: effectively filters out high-frequency modulation noise.

[0041] Feedback drive module: It can provide sufficient drive current to the feedback coil to ensure a fast response of the feedback magnetic field.

[0042] The digital circuit module includes: a clock synchronization module, a phase-sensitive demodulation module, a digital integration module, a 1-bit igma-delta modulation module, a downsampling module, a digital low-pass filter module, and a data transmission module.

[0043] Clock synchronization module: generates excitation clock signal and demodulated square wave signal to ensure synchronous and stable signal output.

[0044] Phase-sensitive demodulation module: realizes a square wave reference signal that is from the same source as the excitation signal, extracts even harmonic components from the digital signal output by the AD converter, and suppresses odd harmonics and high-frequency noise.

[0045] Digital Integrator Module: Implements cumulative smoothing processing to output stable magnetic field data.

[0046] 1-bit sigma-delta modulation module: A fifth-order single-loop sigma-delta modulator is built in the FPGA to quantize multi-bit digital signals into a 1-bit PWM data stream, and the high-frequency noise distribution is optimized through noise shaping technology.

[0047] Downsampling module: Reduces the speed of the high-speed sampled signal.

[0048] Digital low-pass filter module: filters out out-of-band high-frequency noise.

[0049] Data transmission module: The processed magnetic field data is packaged according to a custom protocol and output to the host computer via serial communication. The host computer receives and parses the data through a serial port assistant.

[0050] The workflow and signal processing flow of a 1-bit digital fluxgate system are as follows: Figure 2 As shown, the specific situation is as follows: When the system is in operation, the clock synchronization module of the digital circuit module generates a stable clock signal, which is transmitted to the excitation module of the analog circuit module. The excitation module outputs a constant excitation current to the excitation coil of the sensor probe, generating a periodic excitation magnetic field that causes the magnetic core to saturate alternately.

[0051] At this time, the signal coil of the sensor probe senses the magnetic field of the external environment and outputs a weak signal containing magnetic field information. This signal is amplified by the preamplifier and then transmitted to the AD converter (ADC) to be converted into a digital signal.

[0052] The digital signal is transmitted to the digital circuit module. First, the phase-sensitive demodulation module extracts the second harmonic component and suppresses high-frequency noise. Then, the digital integration module performs accumulation and smoothing processing to obtain stable data.

[0053] The integrated data is not only input to the 1-bit sigma-delta modulation module and quantized into a 1-bit PWM data stream, but also passes through a downsampling module and a digital low-pass filter module to filter out high-frequency noise and downsample, so as to obtain magnetic field data that meets the requirements.

[0054] After the magnetic field data is collected and processed, magnetic field detection is achieved.

[0055] The digital signal output by the 1-bit sigma-delta modulation module is converted into an analog signal by a DA converter (DAC), then filtered by an analog low-pass filter, and finally driven by the feedback drive module to generate a feedback magnetic field, so that the sensor core works in a zero magnetic state, forming a closed-loop control.

[0056] It is worth noting that in the embodiments of the above system, the modules included are divided according to functional logic, but are not limited to the above division, as long as the corresponding functions can be achieved; in addition, the specific names of each functional module are only for easy differentiation and are not used to limit the scope of protection of the present invention.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter, characterized in that, The system includes: a sensor probe, an analog circuit module, and a digital circuit module; wherein... The sensor probe is a single-axis fluxgate sensor, which includes a magnetic core and an excitation coil, a signal coil and a feedback coil wound around the magnetic core. It is used to sense the magnitude and direction of the ambient magnetic field, output the measured magnetic field signal to the analog circuit module, and receive excitation current and feedback current to maintain the working state of the magnetic core. The analog circuit module is used to generate excitation current, amplify and convert the received magnetic field signal into an analog-to-digital signal, and also to convert, filter and drive the signal output by the digital circuit module into an analog-to-digital signal, and output feedback current to the feedback coil of the sensor probe. The digital circuit module, implemented on an FPGA, is used to process the digital signal after analog-to-digital conversion, including phase-sensitive demodulation, digital integration, 1-bit sigma-delta modulation, downsampling, and digital low-pass filtering. It outputs the processed magnetic field detection data to the host computer and simultaneously generates a synchronous clock signal to the analog circuit module.

2. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 1, characterized in that, The analog circuit module includes: an excitation module, a preamplifier, an AD converter, an analog low-pass filter, and a feedback drive module; wherein... The excitation module is used to receive the synchronous clock signal generated from the digital circuit module, generate an excitation current, and provide it to the excitation coil to generate a periodic excitation magnetic field signal. The preamplifier is used to connect to the signal coil and amplify the induced signal; The AD converter is used to convert the amplified induced signal into a digital signal and output it to the digital circuit module. The analog low-pass filter is used to filter out high-frequency modulation noise; The feedback drive module is used to provide feedback current to the feedback coil, ensuring that the magnetic core works in a zero magnetic state and completing the negative feedback operation.

3. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 2, characterized in that, The preamplifier is a low-power instrumentation amplifier, and a fixed gain is set for the signal output from the signal coil.

4. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 2, characterized in that, The feedback drive module uses a low-noise precision operational amplifier to drive the feedback coil to generate a compensating magnetic field that is opposite to the direction of the external magnetic field, ensuring that the magnetic core works in a zero-magnetic state.

5. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 2, characterized in that, The digital circuit module includes: a clock synchronization module, a phase-sensitive demodulation module, a digital integration module, a 1-bit sigma-delta modulation module, a downsampling module, a digital low-pass filter, and a data transmission module; wherein, The clock synchronization module is used to generate a synchronous clock signal to the excitation module, and also to generate a demodulated square wave signal to output to the phase-sensitive demodulation module; The phase-sensitive demodulation module is used to extract even-order harmonic components from the output signal of the AD converter and suppress high-frequency noise. The digital integration module is used to perform cumulative smoothing processing on the instantaneous signal output by the phase-sensitive demodulation module; The 1-bit sigma-delta modulation module is used to quantize the signal output by the digital integrator module into a 1-bit digital stream; The downsampling module is used to reduce the data rate of the signal output by the digital integration module; The digital low-pass filter module is used to filter out out-of-band high-frequency noise from the signal output by the downsampling module; The data transmission module is used to send the magnetic field detection data processed by the digital low-pass filter module to the host computer via a serial port.

6. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 5, characterized in that, The 1-bit sigma-delta modulation module adopts a high-order single-loop modulator structure and uses noise shaping technology to push quantization noise to the high-frequency band in order to improve the signal-to-noise ratio and linearity within the signal bandwidth.

7. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 6, characterized in that, The higher-order single-loop modulator is a fifth-order single-loop sigma-delta modulator.

8. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 5, characterized in that, The clock synchronization module generates two clock signals from the same source, which are used for the excitation module and the phase-sensitive demodulation module respectively, to ensure the synchronization of excitation and demodulation.

9. The digital fluxgate magnetometer system based on a 1-bit sigma-delta digital-to-analog converter according to claim 1, characterized in that, The magnetic core is made of permalloy material, which is used to reduce hysteresis loss and improve magnetic field induction sensitivity.

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