Automatic gain calibration method and system for analog front end of very low frequency detection system

Abstract

The invention provides a very low frequency detection system analog front end gain automatic calibration method and system, and the method comprises the steps: generating a calibration signal sequence based on the calibration total time limit and the sweep frequency signal period of an analog front end circuit; performing data acquisition on the calibration signal sequence to obtain sampling data; performing signal analysis on the sampling data to obtain circuit gain of each frequency sweep point, and determining a change curve of each frequency sweep signal gain along with frequency; and performing linear interpolation based on the circuit gain of each frequency sweeping point to obtain a gain change curve corresponding to the analog front-end circuit. According to the invention, the actual circuit gain of the detection system at each frequency point is accurately obtained, so that the reduction precision of the real intensity of the received signal is remarkably improved, and the problem of insufficient accuracy in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of low-frequency fluctuation detection, and in particular to a method and system for automatically calibrating the gain of an analog front end of a very low frequency detection system. Background Art

[0002] The D layer of the ionosphere is located at an altitude of 60 to 90 kilometers above the earth's surface. Due to its low altitude and low electron concentration, it is difficult for traditional detection systems to achieve long-term, continuous and effective observation of it. However, extremely low frequency (ELF, 3 Hz to 3 kHz) and very low frequency (VLF, 3 kHz to 30 kHz) radio waves, with a wide frequency range of 300 Hz to 100 kHz and a long wavelength, carry a large amount of important information related to the D layer of the ionosphere when they are repeatedly reflected in the earth-ionosphere waveguide. Therefore, remote sensing detection of the D layer of the ionosphere using ELF / VLF radio waves has become a key research direction. In this context, ground-based ELF / VLF detection systems have played an important role. These systems can accurately measure the intensity of the magnetic field component of the electromagnetic wave reaching the detection equipment, which contains key information about the influence of the D layer of the ionosphere when the electromagnetic wave propagates in the earth-ionosphere waveguide, thereby providing researchers with high-value detection data related to the D layer of the ionosphere. These data are crucial for analyzing the propagation characteristics of radio waves and revealing the physical characteristics of the ionosphere D layer. However, accurately restoring the true strength of the received signal is still a key issue that needs to be solved. The accuracy of signal strength restoration directly affects the credibility of the detection data, which in turn determines the scientificity and accuracy of the study of the characteristics of the ionosphere D layer. Solving this problem is of great significance for promoting the development of extremely low frequency / very low frequency detection technology and in-depth research on the ionosphere D layer.

[0003] In extremely low frequency (ELF) and very low frequency (VLF) detection systems, the difference in circuit gain at each frequency point is one of the main factors affecting the accuracy of signal restoration. This difference mainly comes from two reasons: First, since the components used in the circuit are not ideal components, there are parameter deviations and nonlinear characteristics, which lead to inconsistent circuit gains at each signal channel and frequency point, such as manufacturing deviations of amplifier gain or offsets of filter frequency response. Secondly, in actual operation, environmental factors (such as temperature, humidity, etc.) will affect the performance of circuit components, causing parameter drift of components such as resistors and capacitors, thereby causing unpredictable changes in circuit gain. In addition, in order to minimize the impact of power frequency interference and human activities, ELF / VLF detection systems are usually deployed in areas with few people or extreme environmental conditions, and operate in an unattended manner. This makes it impractical to perform on-site circuit gain calibration using traditional standard signal sources, oscilloscopes or spectrum analyzers.

[0004] For the problem of poor accuracy of existing very low frequency detection methods, no effective solution has been proposed yet. Summary of the Invention

[0005] The present invention provides a method and system for automatically calibrating the gain of the analog front end of a very low frequency detection system to solve the defect of poor accuracy of existing very low frequency detection methods.

[0006] In a first aspect, the present invention provides a method for automatically calibrating the gain of the analog front end of a very low frequency detection system, including: Generating a calibration signal sequence based on the total calibration time limit of the analog front end circuit and the sweep signal period; Collecting data on the calibration signal sequence to obtain sampled data; Analyzing the signals of the sampled data to obtain the circuit gain at each sweep frequency point and determining the change curve of the gain of each sweep signal with frequency; Based on the circuit gain at each sweep frequency point, performing linear interpolation to obtain the gain change curve corresponding to the analog front end circuit.

[0007] According to the method for automatically calibrating the gain of the analog front end of a very low frequency detection system provided by the present invention, generating a calibration signal sequence based on the total calibration time limit of the analog front end circuit and the sweep signal period includes: Combining the total calibration time limit of the analog front end circuit and the sweep signal period, dividing the sweep frequency range into several frequency bands; For each of the frequency bands, setting corresponding sweep parameters; Obtaining the control word corresponding to the sweep parameter of each frequency band and generating the calibration signal sequence based on the control word.

[0008] According to the method for automatically calibrating the gain of the analog front end of a very low frequency detection system provided by the present invention, collecting data on the calibration signal sequence to obtain sampled data includes: Adjusting the amplitude of the calibration signal sequence; Sampling the amplitude-adjusted calibration signal sequence to obtain the sampled data.

[0009] According to the method for automatically calibrating the gain of the analog front end of a very low frequency detection system provided by the present invention, analyzing the signals of the sampled data to obtain the circuit gain at each sweep frequency point and determining the change curve of the gain of each sweep signal with frequency includes: Analyzing the signals of the sampled data to obtain the power spectral density distribution map of the signals within the entire sweep frequency range; Based on the power spectral density distribution map, perform energy integration on each of the frequency sweep points to obtain the signal intensity of each of the frequency sweep points; Based on the signal intensity of each of the frequency sweep points, obtain the circuit gain corresponding to the frequency sweep point; Based on the circuit gains corresponding to each of the frequency sweep points, determine the variation curve of the gain of each sweep signal with frequency.

[0010] According to an automatic calibration method for the gain of the analog front end of a very low frequency detection system provided by the present invention, perform signal analysis on the sampling data to obtain the power spectral density distribution map of the signal within the entire frequency sweep range, including: Extract and separate the sampling data in different channels according to the arrangement order during sampling; Simultaneously store the extracted and separated sampling data; Perform FIR filtering and short-time Fourier transform on the sampling data of each channel to obtain the power spectral density distribution map of the signal within the entire frequency sweep range.

[0011] According to an automatic calibration method for the gain of the analog front end of a very low frequency detection system provided by the present invention, based on the power spectral density distribution map, perform energy integration on each of the frequency sweep points to obtain the signal intensity of each of the frequency sweep points, including: For each of the frequency sweep points, subject the calibration signals in several channels to signal conditioning processing to obtain a first signal intensity, and subject the calibration signals in the remaining channels to gain calibration and signal conditioning to obtain a second signal intensity.

[0012] According to an automatic calibration method for the gain of the analog front end of a very low frequency detection system provided by the present invention, based on the signal intensity of each of the frequency sweep points, obtain the circuit gain corresponding to the frequency sweep point, including: Determine the circuit gain corresponding to the frequency sweep point according to the ratio of the second signal intensity to the first signal intensity of the frequency sweep point.

[0013] According to an automatic calibration method for the gain of the analog front end of a very low frequency detection system provided by the present invention, based on the circuit gain of each of the frequency sweep points, perform linear interpolation to obtain the gain variation curve corresponding to the analog front end circuit, including: Perform linear interpolation on the circuit gain of each of the frequency sweep points within the entire frequency sweep range at a preset step size for the frequency, to obtain the gain variation characteristic corresponding to the analog front end circuit when the frequency resolution is the preset step size; Generate the gain variation curve based on the gain variation characteristic of each of the frequency sweep points.

[0014] In a second aspect, the present invention also provides an automatic calibration system for the gain of the analog front end of a very low frequency detection system, including: A magnetic sensor, configured to receive electromagnetic wave signals in the extremely low frequency or very low frequency band and convert the electromagnetic wave signals into electrical signals; A calibration signal sequence generation module, configured to generate a calibration signal sequence; A programmable multi-channel switching module, configured to transmit the electrical signals output by the magnetic sensor or the calibration signals output by the calibration signal sequence generation module; A multi-channel gain to-be-calibrated module, configured to preprocess the calibration signals transmitted by the programmable multi-channel switching module; A long-distance transmission module, configured to transmit the analog signals output by the multi-channel gain to-be-calibrated module to a subsequent processing module over a long distance; A multi-channel acquisition module, configured to condition the analog signals transmitted by the long-distance transmission module and complete data acquisition; An MCU control and processing module, configured to complete the function control of each module, as well as data transmission and processing; A host computer, configured to display the gain calibration result.

[0015] In a third aspect, the present invention further provides an automatic gain calibration device for the analog front end of a very low frequency detection system, including: A generation module, configured to generate a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period; An acquisition module, configured to perform data acquisition on the calibration signal sequence to obtain sampled data; An analysis module, configured to perform signal analysis on the sampled data to obtain the circuit gain at each sweep frequency point and determine the variation curve of the gain of each sweep signal with frequency; A calibration module, configured to perform linear interpolation based on the circuit gain at each sweep frequency point to obtain the gain variation curve corresponding to the analog front-end circuit.

[0016] In a fourth aspect, the present invention further provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the method for automatically calibrating the gain of the analog front end of the very low frequency detection system as described in the first aspect above is implemented.

[0017] In a fifth aspect, the present invention further provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the method for automatically calibrating the gain of the analog front end of the very low frequency detection system as described in the first aspect above is implemented.

[0018] In a sixth aspect, the present invention further provides a computer program product, including a computer program. When the computer program is executed by a processor, the method for automatically calibrating the gain of the analog front end of the very low frequency detection system as described in the first aspect above is implemented.

[0019] Compared with the prior art, the present invention has the following beneficial effects: The method for automatically calibrating the gain of the analog front end of the very low frequency detection system provided by the present invention solves the problem of insufficient accuracy in the prior art by extracting, storing, and amplitude analyzing signals to solve the system gain at specific sweep frequency points and obtaining the in-band full-band gain change curve with a specific frequency resolution through an interpolation method. This method can be automatically calibrated online at any time according to requirements, accurately obtaining the actual circuit gain of the detection system at each frequency point, thereby significantly improving the reduction accuracy of the true intensity of the received signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 is a flowchart of the method for automatically calibrating the gain of the analog front end of the very low frequency detection system provided by the present invention; Figure 2 is a graph showing the calibration result of the analog front end gain in an embodiment of the present invention; Figure 3 is a schematic structural diagram of the system for automatically calibrating the gain of the analog front end of the very low frequency detection system provided by the present invention; Figure 4 is a schematic diagram of the calibration signal sequence generation module in an embodiment of the present invention; Figure 5 is a schematic diagram of the programmed multi-channel switching module in an embodiment of the present invention; Figure 6 is a schematic diagram of the multi-channel data acquisition module in an embodiment of the present invention; Figure 7 is a flowchart of the signal amplitude extraction method of the signal analysis unit in an embodiment of the present invention; Figure 8 is a block diagram of the structure of the device for automatically calibrating the gain of the analog front end of the very low frequency detection system provided by the present invention; Figure 9 is a schematic structural diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] To make the objectives, technical solutions and advantages of the present invention more clear, the following will, in conjunction with the accompanying drawings in the present invention, clearly and completely describe the technical solutions in the present invention. Apparently, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0023] The present invention provides a method for automatically calibrating the gain of the analog front end of a very low frequency detection system. Figure 1 It is a flowchart of the method for automatically calibrating the gain of the analog front end of the very low frequency detection system provided by the present invention. As Figure 1 shown, the method includes the following steps: Step S101, generate a calibration signal sequence based on the total calibration duration limit of the analog front end circuit and the sweep signal period; Step S102, perform data acquisition on the calibration signal sequence to obtain sampled data; Step S103, perform signal analysis on the sampled data to obtain the circuit gain at each sweep frequency point and determine the variation curve of the gain of each sweep signal with frequency; Step S104, perform linear interpolation based on the circuit gain at each sweep frequency point to obtain the gain variation curve corresponding to the analog front end circuit.

[0024] In this method, first, a specific calibration signal sequence is generated based on the total calibration duration limit of the analog front end circuit and the sweep signal period. Then, data acquisition is performed on the calibration signal sequence to obtain sampled data. Next, signal analysis is performed on the sampled data to obtain the circuit gain at each sweep frequency point and determine the variation curve of the gain of each sweep signal with frequency. Finally, a gain variation curve with a specific frequency resolution within the working frequency band is obtained through interpolation with a specific frequency step. In the above process, signal extraction, storage, and amplitude analysis can be completed, the system gain at a specific sweep frequency point can be solved, and a gain variation curve of the entire frequency band within the band with a specific frequency resolution can be obtained by combining the interpolation method. This method can be calibrated automatically online at any time according to requirements, accurately obtain the actual circuit gain of the detection system at each frequency point, thereby significantly improving the reduction accuracy of the true intensity of the received signal and solving the problem of insufficient accuracy in the prior art.

[0025] In some of the embodiments, step S101, generate a calibration signal sequence based on the total calibration duration limit of the analog front end circuit and the sweep signal period, includes: combine the total calibration duration limit of the analog front end circuit and the sweep signal period, divide the sweep range into several frequency bands; for each frequency band, set corresponding sweep parameters; obtain the control word corresponding to the sweep parameters of each frequency band, and generate a calibration signal sequence based on the control word.

[0026] Exemplarily, first, in combination with the total calibration duration limit t total and the sweep signal period T, the sweep range is reasonably segmented. Different frequency bands correspond to different sweep durations. The lower the frequency band, the longer the sweep time. Conversely, the shorter the sweep time. Suppose it is divided into n sweep frequency bands, and the sweep duration t seg for each segment is as follows:

[0027] wherein, , t seg is the sweep duration of each frequency band, and t total is the total calibration duration. Then, for each different sweep frequency band after segmentation, the signal waveform, signal amplitude, sweep mode, sweep step, and sweep duration are set to ensure that the signal at each frequency corresponds to a sufficient sweep time. When the system needs to perform gain calibration on the analog front end, according to the SPI (Serial Peripheral Interface) communication protocol, in combination with the control words corresponding to each sweep parameter, a calibration signal sequence required for subsequent calibration is generated.

[0028] In some of these embodiments, in step S102, data acquisition is performed on the calibration signal sequence to obtain sampled data, including: adjusting the amplitude of the calibration signal sequence; sampling the amplitude-adjusted calibration signal sequence to obtain sampled data.

[0029] Combined with the above embodiments, in step S103, signal analysis is performed on the sampled data to obtain the circuit gain at each sweep frequency point and determine the variation curve of the sweep signal gain with frequency, including: performing signal analysis on the sampled data to obtain the power spectral density distribution map of the signal within the entire sweep range; based on the power spectral density distribution map, performing energy integration on each sweep frequency point to obtain the signal intensity at each sweep frequency point; based on the signal intensity at each sweep frequency point, obtaining the circuit gain corresponding to the sweep frequency point; based on the circuit gains corresponding to each sweep frequency point, determining the variation curve of the sweep signal gain with frequency.

[0030] Specifically, performing signal analysis on the sampled data to obtain the power spectral density distribution map of the signal within the entire sweep range includes: extracting and separating the sampled data in different channels according to the arrangement order during sampling; simultaneously storing the extracted and separated sampled data; performing FIR filtering and short-time Fourier transform on the sampled data of each channel to obtain the power spectral density distribution map of the signal within the entire sweep range.

[0031] More specifically, based on the power spectral density distribution map, energy integration is performed on each frequency sweep point to obtain the signal intensity of each frequency sweep point, including: for each frequency sweep point, the calibration signals of several channels are processed through signal conditioning to obtain the first signal intensity, and the calibration signals of the remaining channels are processed through gain calibration and signal conditioning to obtain the second signal intensity.

[0032] Based on the signal intensity of each frequency sweep point, the circuit gain corresponding to the frequency sweep point is obtained, including: determining the circuit gain corresponding to the frequency sweep point according to the ratio of the second signal intensity to the first signal intensity of the frequency sweep point.

[0033] Exemplarily, first, the sampled data in three channels are extracted and separated from the ELF / VLF original sampled data containing three-channel signals according to the arrangement order during sampling. For the sampled data of each channel extracted and separated, the sampled data of the three channels are stored simultaneously to ensure that the sampled data of the three channels can be strictly aligned in time, and to ensure that the acquisition times of the three data points with the same serial number in the three channels are the same.

[0034] Then, FIR (Finite Impulse Response) filtering is performed on the three-channel data, the window function window_fun is selected, the target data is segmented according to the window length, and the number of overlapping points N between segments is determined. overlap And the step size Step is set, and the number of points N for performing the Fourier transform is set. fft , based on the sweep bandwidth B width and the sampling frequency f s The short-time Fourier transform is performed on the three-channel sampled data to solve the power spectral density distribution map of the signal within the entire sweep bandwidth.

[0035] Based on the obtained signal power spectral density distribution map, energy integration is performed on each frequency sweep point within the bandwidth △B to obtain the signal intensity of each frequency sweep point for the three channels. For the i-th frequency sweep point, the signal intensity A obtained for one channel is the signal intensity after the calibration signal is only processed through signal conditioning. 0,i , and the signal intensity A obtained for the other two channels is the signal intensity after the calibration signal is jointly processed through multi-channel gain calibration and signal conditioning. ch,i (ch represents the analog front-end serial number), so that the signal intensities of the three channels at the same frequency point can be obtained.

[0036] For the frequency sweep point f i , by using the signal intensity A ch,i compared with the signal intensity A 0,i , the circuit gain G corresponding to this frequency point can be obtained. ch,i , thereby obtaining the curve of the circuit gain varying with frequency within the entire sweep band. Among them, the circuit gain corresponding to each frequency sweep point of the analog front-end in the multi-channel gain to be calibrated module is:

[0037] Among them, 。

[0038] In some of these embodiments, in step S104, based on the circuit gain of each frequency sweep point, linear interpolation is performed to obtain the gain change curve corresponding to the analog front-end circuit, including: for the circuit gain of each frequency sweep point within the entire frequency sweep range, linear interpolation is performed on the frequency according to a preset step size to obtain the gain change characteristic corresponding to the analog front-end circuit when the frequency resolution is the preset step size; and a gain change curve is generated based on the gain change characteristic of each frequency sweep point.

[0039] Exemplarily, based on the circuit gains of each frequency point within the entire frequency sweep range, linear interpolation is performed on the frequency according to the required step size f step to obtain the gain change characteristic corresponding to the analog front-end circuit when the frequency resolution is f step 。

[0040] To verify the effectiveness of the above method, an analog front-end gain calibration experiment was carried out using the above method. Figure 2 is the analog front-end gain calibration result diagram in the embodiments of the present invention. As Figure 2 shown in the figure, the abscissa is the frequency, the ordinate is the normalized gain of the circuit of the system to be calibrated. The solid line represents the system standard gain, that is, the normalized value of the actual gain of the system circuit tested by a standard instrument. The dashed line represents the system circuit gain calibration result obtained by using the analog front-end gain calibration method in this example. Through comparative analysis, it can be found that the working frequency band in this example is 300 Hz - 100 kHz, and the calibration result shows that the normalized change trend of the system gain in the entire frequency band is almost exactly the same as the normalized value change trend of the system standard gain tested by the standard instrument. Further analysis shows that the average value of the difference between the two normalized gains is 0.0061, and the relative error is about 0.6%; the standard deviation of the error between the two in the entire frequency band is about 0.0039, and the calibration error in the entire frequency band can basically be well controlled within 1%. It can be seen that the system and method for remotely online automatic calibration of the analog front-end gain constructed in this example can accurately obtain the true gain of the system circuit at each frequency point within the entire passband at any time, remotely online, and automatically.

[0041] The present invention also provides an analog front-end gain automatic calibration system for a very low frequency detection system. Figure 3 is the structural schematic diagram of the analog front-end gain automatic calibration system for the very low frequency detection system provided by the present invention. As Figure 3 shown in the figure, this system includes: A magnetic sensor, configured to receive electromagnetic wave signals in the extremely low frequency or very low frequency band in nature and convert the electromagnetic wave signals into electrical signals; A calibration signal sequence generation module, which is used to generate a calibration signal sequence; A programmable multi-channel switching module, which is connected to the magnetic sensor and the calibration signal sequence generation module, and is used to transmit the electrical signal output by the magnetic sensor or the calibration signal output by the calibration signal sequence generation module; A multi-channel gain to-be-calibrated module, which is electrically connected to the programmable multi-channel switching module, and is used to perform preprocessing such as filtering, amplification, and single-ended to differential-ended conversion on the calibration signal transmitted by the programmable multi-channel switching module; A long-distance transmission module, which is electrically connected to the multi-channel gain to-be-calibrated module, and is used to transmit the analog signal output by the multi-channel gain to-be-calibrated module to the subsequent processing module over a long distance; A multi-channel acquisition module, which is electrically connected to the long-distance transmission module, and is used to condition the analog signal transmitted by the long-distance transmission module and complete data acquisition; An MCU control and processing module, which is electrically connected to the calibration signal sequence generation module, the programmable multi-channel switching module, and the multi-channel data acquisition module, and is used to complete the function control of each module, as well as data transmission and processing; A host computer, which is used to display the gain calibration result.

[0042] When this system is in use, the calibration signal sequence generation module generates a specific calibration signal sequence. Under the action of the programmable multi-channel switching module, the calibration signal sequence is input into the multi-channel gain to-be-calibrated module and then transmitted to the multi-channel acquisition module through the long-distance transmission module to complete data acquisition; the MCU (Microcontroller Unit) control and processing module performs signal analysis, solves the power spectral density distribution map of the signal within the entire sweep frequency range, solves the signal intensity through energy integration within a specific frequency bandwidth, and obtains the change curve of the gain of each sweep signal with frequency; finally, the gain change curve with a specific frequency resolution within the working frequency band of the system is obtained through interpolation with a specific frequency step, and the display is completed on the host computer.

[0043] It should be noted that the calibration signal sequence generation module includes a clock generation unit and a DDS (Direct Digital Synthesizer) signal generation unit. The calibration signal sequence generation module can generate the calibration signal sequence required for calibration through the clock generation unit and the DDS signal generation unit.

[0044] Specifically, the clock generation unit generates a standard clock signal, which provides a high-precision clock source for the normal operation of the module and signal generation; the DDS signal generation unit generates sweep signals with different durations in different segments according to different calibration signal periods. The longer the period, the longer the sweep time, and vice versa, the shorter the sweep time.

[0045] The programmable multi-channel switching module contains three programmable multi-channel switching units. Two of the switching units are respectively connected to the analog front-ends in the multi-channel gain band calibration module, and then connected to the long-distance transmission module. The other switching unit is directly connected to the long-distance transmission module.

[0046] Specifically, when the programmable multi-channel switching unit is connected to the analog front-end, the calibration signal needs to undergo preprocessing of filtering and amplification in the analog front-end, and then be transmitted to the multi-channel acquisition module through the long-distance transmission module. The signal contains the gain information in the analog front-end; when the programmable multi-channel switching unit is directly connected to the long-distance transmission module, the calibration signal is directly transmitted to the multi-channel acquisition module through the long-distance transmission module.

[0047] In this embodiment, two magnetic sensors and the calibration sequence generation module are respectively connected to the switching units in the programmable multi-channel switching module, and are used to receive external electromagnetic signals during normal operation; the calibration signal sequence generation module is connected to the three programmable multi-channel switching modules, and provides a homologous calibration signal sequence for each channel during calibration. Then, two of the programmable multi-channel switching units in the programmable multi-channel switching module are respectively connected to two analog front-ends in the multi-channel gain to-be-calibrated module, and the signal is input into the analog front-end for preprocessing of filtering and amplification; one programmable multi-channel switching unit is directly connected to the long-distance transmission module. Next, the long-distance transmission module transmits the three-way signals to the multi-channel data acquisition module, and the data acquisition module conditions each signal and performs data acquisition under the control of the MCU control and processing module. Finally, the MCU control and processing module analyzes the sampled data input by the multi-channel data acquisition module to obtain the gain characteristic curve of the circuit, and displays it on the upper computer.

[0048] Figure 4 It is a schematic diagram of the calibration signal sequence generation module of the embodiment of the present invention. As Figure 4 shown, the calibration signal sequence generation module includes a clock generation unit and a DDS signal generation unit. The system clock required for the operation of the DDS signal generation unit is generated by the clock generation unit. The accuracy of the clock signal generated by the clock generation unit will largely affect the accuracy of the signal generated by the DDS signal generation unit. When selecting the chip of the clock generation unit, it is necessary to ensure the accuracy of the output signal. A first capacitor C1 needs to be connected to the output end of the clock generation unit. The main function of the capacitor is to filter the output signal of the clock generation unit, so as to obtain a cleaner clock signal for the use of the DDS signal generation unit.

[0049] Continue to refer to Figure 4, the DDS signal generation unit operates with the clock signal generated by the clock generation unit as the working clock. The frequency of the clock signal affects the resolution and accuracy of the signal generated by the DDS signal generation module. The MCU control and processing module controls the DDS signal generation unit through the SPI protocol, writes the corresponding control word into the DDS signal generation unit according to the frequency, waveform, and working mode required by the user, and then the DDS signal generation unit starts to work according to the written parameters and outputs the corresponding signal. The Cap terminal of the DDS signal generation unit needs to be grounded through the second capacitor C2 and the third capacitor C3. The main function of these two capacitors is decoupling, filtering out the high-frequency noise contained in the signal, so as to ensure that the signal is more stable and clean.

[0050] Figure 5 is a schematic diagram of the programmable multi-channel switching module according to an embodiment of the present invention. As Figure 5 shown, the programmable multi-channel switching module includes three programmable channel switching units, and each programmable channel switching unit includes a triode control unit and a channel selection unit respectively. The channel selection unit is used to set the connection between the analog front end in the gain to be calibrated module and the magnetic sensor and the calibration sequence generation module; the triode control unit mainly controls the power supply of the channel selection unit, and changes the connection relationship between the analog front end in the gain to be calibrated module and the magnetic sensor and the calibration sequence generation module by whether to supply power to the channel selection unit.

[0051] The triode control unit is connected to the MCU control and processing module, controls whether the triode is turned on by inputting high and low level signals, and then controls the connection status of the channel selection unit. The channel selection unit is respectively connected to the magnetic sensor, the calibration signal sequence generation module, and the multi-channel gain to be calibrated module, and is used to select the connection between the multi-channel gain to be calibrated module and the magnetic sensor or the calibration signal sequence generation module. The long-distance transmission module is used to connect the multi-channel gain to be calibrated module and the multi-channel data acquisition module. The length of the long-distance transmission module is dozens of meters, or even hundreds of meters, and differential signal transmission is carried out using a twisted pair with an outer shielding layer.

[0052] Specifically, taking the programmable channel switching unit 1 as an example, Vcc is the power supply port, one end is connected to the power supply, and the other end is electrically connected to the collector of the triode Q1 in the triode control unit. In3 is electrically connected to the magnetic sensor, In4 is electrically connected to the calibration sequence generation module, and Out3 is electrically connected to the analog front end in the gain to be calibrated module.

[0053] It should be noted that the signal relay selected by the channel selection unit is a dual-channel. In this embodiment, a structure of using two channels in parallel is adopted, which can reduce the impedance to half of that in the single-channel structure and greatly reduce the energy loss during signal transmission.

[0054] Continue to refer to Figure 5, taking the program-controlled channel switching unit 1 as an example, the triode Q1 should be an NPN-type triode. The base of the triode is electrically connected to the MCU control and processing module through the first resistor R1. Here, the first resistor R1 is for current limiting to prevent the triode from being broken down due to excessive signal current on the base path. The second resistor R2 is a pull-down resistor. One end of the second resistor R2 is electrically connected to the MCU control and processing module, and the other end is electrically connected to the emitter of the triode Q1 to ensure that the triode Q1 is in the cut-off state when the MCU control and processing module has no operation, preventing misoperation caused by the triode Q1 being turned on due to noise or interference signals.

[0055] Figure 6 is a schematic diagram of the multi-channel data acquisition module according to an embodiment of the present invention. As Figure 6 shown, the multi-channel data acquisition module includes data acquisition of three channels, and the data acquisition of each channel includes a signal conditioning unit and a signal sampling unit.

[0056] Specifically, taking the signal conditioning unit 1 as an example, the signal conditioning unit 1 is a differential input structure. The eighth resistor R8 and the ninth resistor R9 are selected as precision resistors with high precision and low temperature drift. One end of the eighth resistor R8 and the ninth resistor R9 is respectively electrically connected to the output of the analog front end through the long-distance transmission module, and the other end is respectively connected to the signal input of the ADC driver chip; the seventh resistor R7 and the tenth resistor R 10 are selected as precision resistors with high precision and low temperature drift. One end of the seventh resistor R7 and the tenth resistor R 10 is electrically connected to the eighth resistor R8 and the ninth resistor R9 and connected to the signal input of the ADC driver chip, and the other end is connected to the feedback input of the ADC driver chip to output differential signals OutP1 and OutN1. The gain setting of the signal adjustment is:

[0057]

[0058] wherein, A1 represents the gain of the positive-phase signal of the differential signal, and A2 represents the gain of the negative-phase signal of the differential signal.

[0059] Specifically, in the program-controlled multi-channel switching module, two paths of the program-controlled multi-channel switching unit are electrically connected to the multi-channel gain to-be-calibrated module through the long-distance transmission module; one path is directly electrically connected to the multi-channel data acquisition module through the long-distance transmission module.

[0060] Continue to refer to Figure 6 , taking the signal sampling unit 1 as an example, the sampling chip is selected as a high-digit and high-sampling rate chip with a differential input structure, which can ensure high time resolution while ensuring the efficiency and convenience of the MCU control and processing module in organizing and transmitting data of each channel.

[0061] Figure 7 is a flowchart of the signal amplitude extraction method of the signal analysis unit according to an embodiment of the present invention. As Figure 7 shown, the method mainly includes the following steps: obtaining high-quality ELF / VLF original sampling data including three-channel data through a multi-channel data acquisition module; extracting the sampling data of each channel to complete the data separation of each channel, and obtaining the sampling data corresponding to each channel; for the sampling data of each channel, storing the data of each channel simultaneously based on a homologous clock to meet the subsequent processing requirements; performing a short-time Fourier transform on the data and solving the power spectral density distribution result of the swept-frequency signal; calculating the amplitude size of the swept-frequency signal within each swept-frequency time period, obtaining the intensity of the swept-frequency signal, and obtaining the amplitudes of the signals of the three channels, where two are the signal intensities of the gain-to-be-calibrated channels and one is the intensity of the calibration reference signal; obtaining the gain at the corresponding frequency point by comparing the signal intensity of the gain-band calibration channel with the intensity of the calibration reference signal, and obtaining the gain at each frequency point of the swept-frequency signal through frequency traversal, that is, the gain change curve; finally, performing linear interpolation on the obtained results with a required specific frequency resolution to obtain the gain change curve within the entire detection frequency band of the detection system. It is possible to obtain the true circuit gain of the detection system within the entire frequency band anytime, anywhere, remotely and online, providing important support for the subsequent inversion calculation of the true intensity of the received signal, and significantly improving the accuracy of the inversion calculation.

[0062] It should be noted that when storing the sampling data of each channel, it must be based on a homologous high-precision clock. Only in this way can it be ensured that the data stored at each time point on each channel corresponds to the same true sampling time, thereby ensuring the authenticity of the final obtained gain result.

[0063] In summary, the present invention designs a method and system for remotely online automatic calibration of the analog front-end gain of a very low frequency detection system, and coordinates the normal working state and calibration state of the system through the MCU control and processing module. During the calibration process, the multi-channel switching module inputs the calibration signal and the reference signal into the multi-channel gain-to-be-calibrated module and the multi-channel data acquisition module respectively to complete the filtering, amplification, acquisition and analysis of the signals. The MCU module calculates the gain parameters of the target frequency point using digital signals and generates the gain change curve within the entire passband through an interpolation method, and finally transmits the result to the upper computer for display. The present invention can achieve remote online automatic calibration anytime, anywhere according to requirements, accurately provide the actual circuit gain of each frequency point, effectively improve the problem of low reduction accuracy of the received signal intensity, and provide a reliable guarantee for the detection task in the extremely low frequency / very low frequency band.

[0064] The innovation of the present invention is mainly reflected in its ability of remote online calibration. Without relying on external instrument equipment, it can complete multi-channel high-precision calibration in an unattended environment in real time, greatly improving the calibration efficiency and flexibility. In addition, by comparing the calibration reference signal with the target signal and combining with the interpolation algorithm, the system generates a high-resolution gain change curve, significantly improving the reduction accuracy of the true signal intensity. These characteristics make it particularly suitable for detection tasks deployed in remote or extreme environments, providing important technical support for studying the propagation characteristics of signals in the Earth-ionosphere waveguide and the dynamic characteristics of the D layer of the ionosphere.

[0065] Furthermore, the present invention can be further improved to enhance its performance. For example, improving the stability and adaptability of the system in extreme environments; expanding the frequency coverage range by optimizing the hardware and algorithms to meet the requirements of more complex application scenarios; introducing intelligent technologies to improve the dynamic prediction and compensation capabilities for gain changes; and realizing flexible system upgrades through modular design. These improvements will further expand the application scope of the present invention and lay a solid foundation for the development of extremely low frequency / very low frequency detection technologies.

[0066] The present invention also provides an automatic calibration device for the analog front-end gain of a very low frequency detection system. The following describes the automatic calibration device for the analog front-end gain of the very low frequency detection system provided by the present invention. The automatic calibration device for the analog front-end gain of the very low frequency detection system described below can be correspondingly referred to the automatic calibration method for the analog front-end gain of the very low frequency detection system described above. Figure 8 is the structural block diagram of the automatic calibration device for the analog front-end gain of the very low frequency detection system provided by the present invention, as Figure 8 shown, the device includes: A generation module 801, configured to generate a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period; An acquisition module 802, configured to perform data acquisition on the calibration signal sequence to obtain sampled data; An analysis module 803, configured to perform signal analysis on the sampled data to obtain the circuit gain at each sweep frequency point and determine the change curve of the gain of each sweep signal with frequency; A calibration module 804, configured to perform linear interpolation based on the circuit gain at each sweep frequency point to obtain the gain change curve corresponding to the analog front-end circuit.

[0067] When this device is in use, first, the generation module 801 generates a specific calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period. Then, the acquisition module 802 performs data acquisition on the calibration signal sequence to obtain sampled data. Next, the parsing module 803 performs signal parsing on the sampled data to obtain the circuit gain at each sweep frequency point and determines the variation curve of each sweep signal gain with frequency. Finally, the calibration module 804 obtains the gain variation curve with a specific frequency resolution within the working frequency band through interpolation with a specific frequency step. In the above process, signal extraction, storage, and amplitude parsing can be completed, the system gain at a specific sweep frequency point can be solved, and the in-band full-band gain variation curve with a specific frequency resolution can be obtained by combining the interpolation method. This device can perform online automatic calibration at any time according to requirements, accurately obtain the actual circuit gain of the detection system at each frequency point, thereby significantly improving the reduction accuracy of the true intensity of the received signal and solving the problem of insufficient accuracy in the prior art.

[0068] Figure 9 An example of the physical structure diagram of an electronic device is shown in Figure 9 As shown, the electronic device may include: a processor 901, a communication interface 902, a memory 903, and a communication bus 904. Among them, the processor 901, the communication interface 902, and the memory 903 complete mutual communication through the communication bus 904. The processor 901 can call the logical instructions in the memory 903 to execute the method for automatically calibrating the gain of the analog front-end of the very low frequency detection system. The method includes: Generating a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period; Performing data acquisition on the calibration signal sequence to obtain sampled data; Performing signal parsing on the sampled data to obtain the circuit gain at each sweep frequency point and determining the variation curve of each sweep signal gain with frequency; Performing linear interpolation based on the circuit gain at each sweep frequency point to obtain the gain variation curve corresponding to the analog front-end circuit.

[0069] In addition, when the logical instructions in the above-mentioned memory 903 are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods in various embodiments of the present invention. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs that can store program codes.

[0070] On the other hand, the present invention also provides a computer program product. The computer program product includes a computer program. The computer program can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the automatic calibration method for the gain of the analog front end of the very low frequency detection system provided by the above-mentioned various methods. The method includes: Generating a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period; Performing data acquisition on the calibration signal sequence to obtain sampled data; Performing signal analysis on the sampled data to obtain the circuit gain at each sweep frequency point and determining the change curve of the gain of each sweep signal with frequency; Based on the circuit gain at each sweep frequency point, performing linear interpolation to obtain the gain change curve corresponding to the analog front-end circuit.

[0071] On another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it is implemented to execute the automatic calibration method for the gain of the analog front end of the very low frequency detection system provided by the above-mentioned various methods. The method includes: Generating a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period; Performing data acquisition on the calibration signal sequence to obtain sampled data; Performing signal analysis on the sampled data to obtain the circuit gain at each sweep frequency point and determining the change curve of the gain of each sweep signal with frequency; Based on the circuit gain at each sweep frequency point, performing linear interpolation to obtain the gain change curve corresponding to the analog front-end circuit.

[0072] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative effort.

[0073] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0074] 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 them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An automatic calibration method for the gain of the analog front end of a very low frequency detection system, characterized in that, Including: Generate a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period; Perform data acquisition on the calibration signal sequence to obtain sampled data; Perform signal analysis on the sampled data to obtain the circuit gain at each sweep point and determine the variation curve of the sweep signal gain with frequency; Based on the circuit gain at each sweep point, perform linear interpolation to obtain the gain variation curve corresponding to the analog front-end circuit.

2. The method for automatically calibrating the gain of the analog front end of the very low frequency detection system according to claim 1, wherein Generate a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period, including: Combine the total calibration duration limit of the analog front-end circuit and the sweep signal period to divide the sweep range into several frequency bands; For each frequency band, set corresponding sweep parameters; Obtain the control word corresponding to the sweep parameters of each frequency band and generate the calibration signal sequence based on the control word.

3. The automatic calibration method for the analog front-end gain of the very low frequency detection system according to claim 1, characterized in that Perform data acquisition on the calibration signal sequence to obtain sampled data, including: Adjust the amplitude of the calibration signal sequence; Sample the amplitude-adjusted calibration signal sequence to obtain the sampled data.

4. The automatic calibration method for the gain of the analog front end of the very low frequency detection system according to claim 1, wherein Perform signal analysis on the sampled data to obtain the circuit gain at each sweep point and determine the variation curve of the sweep signal gain with frequency, including: Perform signal analysis on the sampled data to obtain the power spectral density distribution map of the signal within the entire sweep range; Based on the power spectral density distribution map, perform energy integration on each sweep point to obtain the signal strength at each sweep point; Based on the signal strength at each sweep point, obtain the circuit gain corresponding to the sweep point; Based on the circuit gains corresponding to each sweep point, determine the variation curve of the sweep signal gain with frequency.

5. The method for automatically calibrating the gain of the analog front end of the very low frequency detection system according to claim 4, characterized in that Perform signal analysis on the sampled data to obtain the power spectral density distribution map of the signal within the entire sweep range, including: Extract and separate the sampled data in different channels according to the arrangement order during sampling; Simultaneously store the extracted and separated sampled data; Perform FIR filtering and short-time Fourier transform on the sampled data of each channel to obtain the power spectral density distribution map of the signal within the entire sweep range.

6. The method for automatically calibrating the gain of the analog front end of the very low frequency detection system according to claim 5, wherein Based on the power spectral density distribution map, perform energy integration on each sweep point to obtain the signal strength at each sweep point, including: For each sweep point, obtain the first signal strength by subjecting the calibration signals of several channels to signal conditioning, and obtain the second signal strength by subjecting the calibration signals of the remaining channels to gain calibration and signal conditioning.

7. The method for automatically calibrating the gain of the analog front end of the very low frequency detection system according to claim 6, wherein Based on the signal strength at each sweep point, obtain the circuit gain corresponding to the sweep point, including: Determine the circuit gain corresponding to the sweep point according to the ratio of the second signal strength to the first signal strength at the sweep point.

8. The method for automatically calibrating the gain of the analog front end of the very low frequency detection system according to claim 1, characterized in that Based on the circuit gain at each sweep point, perform linear interpolation to obtain the gain variation curve corresponding to the analog front-end circuit, including: Perform linear interpolation on the circuit gain at each sweep point within the entire sweep range with the frequency at a preset step size to obtain the gain variation characteristic corresponding to the analog front-end circuit with a frequency resolution of the preset step size; Generate the gain change curve based on the gain change characteristics of each of the sweep points.

9. An automatic calibration system for the gain of the analog front end of a very low frequency detection system, characterized in that, Comprising: A magnetic sensor for receiving electromagnetic wave signals in the extremely low frequency or very low frequency band and converting the electromagnetic wave signals into electrical signals; A calibration signal sequence generation module for generating a calibration signal sequence; A programmable multi-channel switching module for transmitting the electrical signals output by the magnetic sensor or the calibration signals output by the calibration signal sequence generation module; A multi-channel gain to be calibrated module for preprocessing the calibration signals transmitted by the programmable multi-channel switching module; A long-distance transmission module for long-distance transmitting the analog signals output by the multi-channel gain to be calibrated module to a subsequent processing module; A multi-channel acquisition module for conditioning the analog signals transmitted by the long-distance transmission module and completing data acquisition; An MCU control and processing module for completing the function control of each module, as well as data transmission and processing; A host computer for displaying the gain calibration result.

10. An automatic calibration device for the gain of the analog front end of a very low frequency detection system, characterized in that, Comprising: A generation module for generating a calibration signal sequence based on the total calibration duration limit of the analog front-end circuit and the sweep signal period; An acquisition module for performing data acquisition on the calibration signal sequence to obtain sampled data; An analysis module for performing signal analysis on the sampled data to obtain the circuit gain of each sweep point and determining the change curve of each sweep signal gain with frequency; A calibration module for performing linear interpolation based on the circuit gain of each of the sweep points to obtain the gain change curve corresponding to the analog front-end circuit.

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