A method and system for automatically calibrating the analog front-end gain of a very low frequency detection system

Abstract

The present invention provides a method and system for automatically calibrating the analog front-end gain of a very low frequency detection system. The method comprises: generating a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the frequency 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 of each frequency sweep point, and determining a curve of the gain of each frequency sweep signal varying with frequency; and performing linear interpolation based on the circuit gain of each frequency sweep point to obtain a gain variation curve corresponding to the analog front-end circuit. Through the present invention, the actual circuit gain of the detection system at each frequency point is accurately obtained, thereby significantly improving the accuracy of restoring the true strength of the received signal and solving the problem of insufficient accuracy in the prior art.

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 ionospheric D layer lies at an altitude of 60 to 90 kilometers above Earth's surface. Due to its low altitude and low electron concentration, traditional detection systems struggle to achieve long-term, continuous, and effective observations. However, extremely low frequency (ELF, 3 Hz to 3 kHz) and very low frequency (VLF, 3 kHz to 30 kHz) radio waves, with their wide frequency range of 300 Hz to 100 kHz and long wavelengths, carry a wealth of important information about the ionospheric D layer when repeatedly reflected in the Earth-ionosphere waveguide. Therefore, remote sensing of the ionospheric D layer using ELF / VLF radio waves has become a key research focus. In this context, ground-based ELF / VLF detection systems play a crucial role. These systems precisely measure the intensity of the magnetic field component of electromagnetic waves reaching the detection equipment. This intensity contains crucial information about the influence of the ionospheric D layer on the electromagnetic waves as they propagate through the Earth-ionosphere waveguide, providing researchers with valuable data related to the ionospheric D layer. These data are crucial for analyzing the propagation characteristics of radio waves and revealing the physical properties of the ionospheric D layer. However, accurately restoring the true strength of the received signal remains a key challenge. The accuracy of signal strength restoration directly impacts the credibility of the detection data, and thus determines the scientific and accurate research on the characteristics of the ionospheric D layer. Solving this problem is of great significance for promoting the development of extremely low frequency (ELF) and very low frequency (VLF) sounding technologies and in-depth research on the ionospheric D layer.

[0003] In extremely low frequency (ELF) and very low frequency (VLF) detection systems, circuit gain variability at different frequencies is a major factor affecting signal reconstruction accuracy. This variability stems from two main factors: First, because the components used in the circuits are not ideal, they exhibit parameter deviations and nonlinear characteristics, leading to inconsistent circuit gain across signal channels and frequencies. This can include manufacturing variations in amplifier gain or shifts in filter frequency response. Second, in actual operation, environmental factors (such as temperature and humidity) can affect the performance of circuit components, causing parameter drift in resistors, capacitors, and other components, leading to unpredictable changes in circuit gain. Furthermore, to minimize the impact of power frequency interference and human activity, ELF / VLF detection systems are often deployed in remote areas or under extreme environmental conditions and operate unattended. This makes on-site circuit gain calibration using traditional standard signal sources, oscilloscopes, or spectrum analyzers impractical.

[0004] There is currently no effective solution to the problem of poor accuracy of existing very low frequency detection methods. Summary of the Invention

[0005] The present invention provides a method and system for automatically calibrating the gain of an analog front end of a very low frequency detection system, which are used 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 an analog front-end of a very low frequency detection system, comprising:

[0007] Generate a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the frequency sweep signal period;

[0008] Performing data acquisition on the calibration signal sequence to obtain sampling data;

[0009] Performing signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point, and determining a curve of the gain of each frequency sweep signal versus frequency;

[0010] Based on the circuit gain of each of the frequency sweep points, linear interpolation is performed to obtain a gain change curve corresponding to the analog front-end circuit.

[0011] According to the present invention, a method for automatically calibrating the gain of an analog front-end of a very low frequency detection system is provided. The method generates a calibration signal sequence based on a total calibration time limit of an analog front-end circuit and a frequency sweep signal period, including:

[0012] The frequency sweep range is divided into several frequency bands in combination with the total calibration time limit of the analog front-end circuit and the frequency sweep signal period;

[0013] For each of the frequency bands, setting corresponding frequency sweep parameters;

[0014] A control word corresponding to the frequency sweep parameter of each frequency band is acquired, and the calibration signal sequence is generated based on the control word.

[0015] According to a very low frequency detection system analog front-end automatic gain calibration method provided by the present invention, data acquisition is performed on the calibration signal sequence to obtain sampled data, including:

[0016] performing amplitude adjustment on the calibration signal sequence;

[0017] The calibration signal sequence after amplitude adjustment is sampled to obtain the sampled data.

[0018] According to a very low frequency detection system analog front-end gain automatic calibration method provided by the present invention, signal analysis is performed on the sampled data to obtain the circuit gain of each frequency sweep point, and a curve of the gain of each frequency sweep signal varying with frequency is determined, including:

[0019] Performing signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range;

[0020] Based on the power spectrum density distribution diagram, performing energy integration on each of the frequency sweeping points to obtain the signal strength of each of the frequency sweeping points;

[0021] Based on the signal strength of each of the frequency sweep points, a circuit gain corresponding to the frequency sweep point is obtained;

[0022] Based on the circuit gain corresponding to each of the frequency sweeping points, a curve of the gain of each frequency sweeping signal varying with frequency is determined.

[0023] According to a very low frequency detection system analog front-end automatic gain calibration method provided by the present invention, signal analysis is performed on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range, including:

[0024] Extracting and separating the sampled data in different channels according to the arrangement order at the time of sampling;

[0025] Simultaneously storing the extracted and separated sampling data;

[0026] The sampling data of each channel is subjected to FIR filtering and short-time Fourier transform to obtain the power spectrum density distribution diagram of the signal within the entire frequency sweep range.

[0027] According to a very low frequency detection system analog front-end automatic gain calibration method provided by the present invention, based on the power spectrum density distribution diagram, energy integration is performed on each of the frequency sweep points to obtain the signal strength of each of the frequency sweep points, including:

[0028] For each of the frequency sweep points, calibration signals of several channels are subjected to signal conditioning to obtain a first signal strength, and calibration signals of the remaining channels are subjected to gain calibration and signal conditioning to obtain a second signal strength.

[0029] According to a very low frequency detection system analog front-end automatic gain calibration method provided by the present invention, based on the signal strength of each frequency sweep point, a circuit gain corresponding to the frequency sweep point is obtained, comprising:

[0030] The circuit gain corresponding to the frequency sweep point is determined according to the ratio of the second signal strength to the first signal strength at the frequency sweep point.

[0031] According to a very low frequency detection system analog front-end gain automatic calibration method provided by the present invention, linear interpolation is performed based on the circuit gain of each frequency sweep point to obtain a gain change curve corresponding to the analog front-end circuit, including:

[0032] For each of the sweep frequency points within the entire sweep frequency range, the frequency is linearly interpolated according to a preset step size to obtain a gain variation characteristic corresponding to the analog front-end circuit when the frequency resolution is the preset step size;

[0033] The gain variation curve is generated based on the gain variation characteristic of each of the frequency sweep points.

[0034] In a second aspect, the present invention further provides a very low frequency detection system analog front-end gain automatic calibration system, comprising:

[0035] A magnetic sensor is used to receive electromagnetic wave signals in the extremely low frequency or very low frequency band and convert the electromagnetic wave signals into electrical signals;

[0036] A calibration signal sequence generating module, used for generating a calibration signal sequence;

[0037] a programmable multi-channel switching module, configured to transmit the electrical signal output by the magnetic sensor or the calibration signal output by the calibration signal sequence generating module;

[0038] A multi-channel gain calibration module, used for pre-processing the calibration signal transmitted by the program-controlled multi-channel switching module;

[0039] A long-distance transmission module, used for transmitting the analog signal output by the multi-channel gain calibration module to a subsequent processing module over a long distance;

[0040] A multi-channel acquisition module, used to condition the analog signal transmitted by the long-distance transmission module and complete data acquisition;

[0041] MCU control and processing module, used to complete the functional control of each module, as well as data transmission and processing;

[0042] Host computer, used to display the gain calibration results.

[0043] In a third aspect, the present invention further provides a very low frequency detection system analog front-end gain automatic calibration device, comprising:

[0044] A generation module, configured to generate a calibration signal sequence based on a total calibration time limit of an analog front-end circuit and a frequency sweep signal period;

[0045] An acquisition module, configured to acquire data from the calibration signal sequence to obtain sampled data;

[0046] An analysis module is used to perform signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point and determine the curve of the gain of each frequency sweep signal as a function of frequency;

[0047] The calibration module is used to perform linear interpolation based on the circuit gain of each of the frequency sweep points to obtain a gain change curve corresponding to the analog front-end circuit.

[0048] In a fourth aspect, the present invention further provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the method for automatically calibrating the analog front-end gain of a very low frequency detection system as described in the first aspect above is implemented.

[0049] In a fifth aspect, the present invention further provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for automatic calibration of the analog front-end gain of a very low frequency detection system as described in the first aspect above.

[0050] In a sixth aspect, the present invention further provides a computer program product, comprising a computer program, which, when executed by a processor, implements the method for automatic calibration of the analog front-end gain of a very low frequency detection system as described in the first aspect above.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The present invention provides an automatic gain calibration method for the analog front-end of a very low frequency detection system. By extracting, storing, and analyzing signal amplitudes, the system gain at specific sweep frequency points is calculated. Combined with an interpolation method, this method generates an in-band, full-band gain curve with a specific frequency resolution. This method enables online, automated calibration anytime, anywhere, as needed, accurately determining the detection system's actual circuit gain at each frequency point. This significantly improves the accuracy of the received signal's true strength, resolving the inaccuracy issues inherent in existing technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0054] Figure 1 This is a flow chart of the automatic calibration method for the analog front-end gain of a very low frequency detection system provided by the present invention;

[0055] Figure 2 2 is a diagram showing the analog front-end gain calibration results in an embodiment of the present invention;

[0056] Figure 3 It is a structural diagram of the automatic calibration system for analog front-end gain of a very low frequency detection system provided by the present invention;

[0057] Figure 4 is a schematic diagram of a calibration signal sequence generating module according to an embodiment of the present invention;

[0058] Figure 5 is a schematic diagram of a program-controlled multi-channel switching module according to an embodiment of the present invention;

[0059] Figure 6 is a schematic diagram of a multi-channel data acquisition module according to an embodiment of the present invention;

[0060] Figure 7 is a flow chart of a signal amplitude extraction method of a signal analysis unit according to an embodiment of the present invention;

[0061] Figure 8 This is a structural block diagram of the automatic calibration device for analog front-end gain of a very low frequency detection system provided by the present invention;

[0062] Figure 9 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0063] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0064] The present invention provides a method for automatically calibrating the gain of an analog front-end of a very low frequency detection system. Figure 1 Flowchart of the method for automatic calibration of analog front-end gain of a very low frequency detection system provided by the present invention. Figure 1 As shown, the method includes the following steps:

[0065] Step S101, generating a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the frequency sweep signal period;

[0066] Step S102, collecting data on the calibration signal sequence to obtain sampled data;

[0067] Step S103, performing signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point, and determining a curve of the gain of each frequency sweep signal versus frequency;

[0068] Step S104 , performing linear interpolation based on the circuit gain at each frequency sweep point to obtain a gain variation curve corresponding to the analog front-end circuit.

[0069] In this method, first, based on the total calibration time limit of the analog front-end circuit and the sweep signal period, a specific calibration signal sequence is generated. Then, data acquisition is performed on the calibration signal sequence to obtain sampled data. The sampled data is then subjected to signal analysis to obtain the circuit gain of each sweep point, and the gain change curve of each sweep signal with frequency is determined. Finally, the gain change curve of a specific frequency resolution within the working frequency band is obtained by interpolation of a specific frequency step. In the above process, signal extraction, storage and amplitude analysis can be completed, the system gain at a specific sweep point can be solved, and the in-band full-band gain change curve of a specific frequency resolution can be obtained by combining the interpolation method. This method can be automatically calibrated online anytime and anywhere according to demand, and the actual circuit gain of the detection system at each frequency point can be accurately obtained, thereby significantly improving the accuracy of restoring the true strength of the received signal and solving the problem of insufficient accuracy in the existing technology.

[0070] In some embodiments, step S101 generates a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the sweep signal period, including: dividing the sweep range into several frequency bands in combination with the total calibration time limit of the analog front-end circuit and the sweep signal period; for each frequency band, setting corresponding sweep parameters; obtaining a control word corresponding to the sweep parameter of each frequency band, and generating a calibration signal sequence based on the control word.

[0071] For example, first, the total calibration time limit t total The sweep range is divided into n sweep ranges and the sweep signal period T. 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 ranges, and the sweep duration of each segment is t seg for:

[0072]

[0073] in, , t seg is the sweep time of each frequency band, t total The total calibration duration is denoted by . Then, for each segmented sweep band, the signal waveform, amplitude, sweep mode, sweep step, and sweep duration are set to ensure a sufficiently long sweep time for each frequency signal. When the system requires gain calibration of the analog front end, the SPI (Serial Peripheral Interface) communication protocol is used, combining the control words corresponding to the sweep parameters to generate the calibration signal sequence required for subsequent calibration.

[0074] In some embodiments, step S102, collecting data on the calibration signal sequence to obtain sampled data, includes: amplitude-adjusting the calibration signal sequence; and sampling the amplitude-adjusted calibration signal sequence to obtain sampled data.

[0075] In combination with the above embodiment, step S103, performing signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point, and determining the curve of the change of each frequency sweep signal gain with frequency, including: performing signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range; based on the power spectrum density distribution diagram, performing energy integration on each frequency sweep point to obtain the signal strength of each frequency sweep point; based on the signal strength of each frequency sweep point, obtaining the circuit gain corresponding to the frequency sweep point; based on the circuit gain corresponding to each frequency sweep point, determining the curve of the change of each frequency sweep signal gain with frequency.

[0076] Specifically, the sampling data is subjected to signal analysis to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range, including: extracting and separating the sampling data in different channels according to the arrangement order at the time of sampling; simultaneously storing the extracted and separated sampling data; performing FIR filtering and short-time Fourier transform on the sampling data of each channel to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range.

[0077] More specifically, based on the power spectrum density distribution diagram, energy integration is performed on each scanning point to obtain the signal strength of each scanning point, including: for each scanning point, the calibration signals of several channels are subjected to signal conditioning processing to obtain a first signal strength, and the calibration signals of the remaining channels are subjected to gain calibration and signal conditioning to obtain a second signal strength.

[0078] Obtaining a circuit gain corresponding to the frequency sweep point based on the signal strength of each frequency sweep point includes determining the circuit gain corresponding to the frequency sweep point according to a ratio of the second signal strength to the first signal strength of the frequency sweep point.

[0079] For example, first, the sampled data for the three channels is extracted and separated from the original ELF / VLF sampled data containing the three-channel signal according to the order in which it was sampled. The sampled data for each channel is then stored simultaneously to ensure strict temporal alignment of the sampled data for the three channels, ensuring that the three data points with the same sequence number across the three channels were collected at the same time.

[0080] Then, perform FIR (Finite Impulse Response) filtering on the three-channel data, select the window function window_fun, and segment the target data according to the window length to determine the number of overlapping points N between the segments. overlap And step size Step, set the number of points N when performing Fourier transformfft , based on the sweep bandwidth B width and sampling frequency f s Perform short-time Fourier transform on the three-channel sampling data to obtain the power spectrum density distribution diagram of the signal within the entire frequency sweep bandwidth.

[0081] Based on the obtained signal power spectrum density distribution diagram, the energy of each sweep point in the bandwidth △B is integrated to obtain the signal strength of each sweep point of the three channels. For the i-th sweep point, the signal strength A obtained by one channel is the signal strength of the calibration signal after signal conditioning processing only. 0,i The other two channels get the signal strength A after the calibration signal is conditioned by multi-channel gain calibration and signal conditioning. ch,i (ch represents the analog front-end serial number). In this way, the signal strength of the same frequency point of the three channels can be obtained.

[0082] For the frequency sweep point f i , using signal strength A ch,i With signal strength A 0,i By comparing, we can get the circuit gain G corresponding to the frequency point. ch,i , thereby obtaining the curve of circuit gain variation with frequency in the entire frequency sweep range. Among them, the circuit gain corresponding to each frequency sweep point of the analog front end in the multi-channel gain calibration module is:

[0083]

[0084] in, .

[0085] In some embodiments, step S104 performs linear interpolation based on the circuit gain of each frequency sweep point to obtain a gain change curve corresponding to the analog front-end circuit, including: performing linear interpolation on the circuit gain of each frequency sweep point within the entire frequency sweep range according to a preset step size to obtain a gain change characteristic corresponding to the analog front-end circuit when the frequency resolution is the preset step size; and generating a gain change curve based on the gain change characteristic of each frequency sweep point.

[0086] For example, based on the circuit gain of each frequency point in the entire sweep range, the frequency is adjusted according to the required step size f step Linear interpolation can be performed to obtain a frequency resolution of f step The gain change characteristics corresponding to the analog front-end circuit are shown.

[0087] In order to verify the effectiveness of the above method, an analog front-end gain calibration experiment was carried out using the above method. Figure 2 FIG. 1 is a diagram showing the analog front-end gain calibration result according to an embodiment of the present invention. Figure 2As shown in the figure, the horizontal axis represents frequency, and the vertical axis represents the normalized gain of the system circuit to be calibrated. The solid line represents the system standard gain, which 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 using the analog front-end gain calibration method in this example. A comparative analysis shows that the operating frequency band in this example is 300 Hz-100 kHz. The calibration results show that the normalized system gain trend across the entire frequency band is almost identical to the normalized system gain trend measured by the standard instrument. Further analysis reveals that the average difference in normalized gain between the two is 0.0061, with a relative error of approximately 0.6%. The standard deviation of the errors across the entire frequency band is approximately 0.0039, and the calibration error across the entire frequency band is generally well controlled within 1%. Therefore, the system and method for remote online automatic calibration of analog front-end gain constructed in this example can accurately and remotely and automatically determine the actual gain of the system circuit at each frequency point within the entire passband, anytime, anywhere.

[0088] The present invention also provides a very low frequency detection system analog front-end gain automatic calibration system, Figure 3 FIG. 1 is a structural diagram of the automatic calibration system for analog front-end gain of a very low frequency detection system provided by the present invention. Figure 3 As shown, the system includes:

[0089] Magnetic sensors are used to receive electromagnetic wave signals in extremely low frequency or very low frequency bands in nature and convert the electromagnetic wave signals into electrical signals;

[0090] A calibration signal sequence generating module, used for generating a calibration signal sequence;

[0091] A programmable multi-channel switching module is connected to the magnetic sensor and the calibration signal sequence generating module, and is used to transmit the electrical signal output by the magnetic sensor or the calibration signal output by the calibration signal sequence generating module;

[0092] The multi-channel gain calibration module is electrically connected to the programmable multi-channel switching module and is used to perform pre-processing such as filtering, amplification, and single-ended to double-ended conversion on the calibration signal transmitted by the programmable multi-channel switching module;

[0093] A long-distance transmission module is electrically connected to the multi-channel gain calibration module and is used to transmit the analog signal output by the multi-channel gain calibration module to a subsequent processing module over a long distance;

[0094] The multi-channel acquisition module 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;

[0095] The MCU control and processing module is electrically connected to the calibration signal sequence generation module, the programmable multi-channel switching module, and the multi-channel data acquisition module to complete the functional control of each module, as well as data transmission and processing;

[0096] Host computer, used to display the gain calibration results.

[0097] 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 calibration 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 spectrum density distribution diagram of the signal within the entire frequency sweep range, solves the signal strength by integrating the energy within a specific bandwidth, and obtains the gain change curve of each frequency sweep signal with frequency; finally, the gain change curve of the system with a specific frequency resolution within the working frequency band is obtained by interpolation of a specific frequency step size, and is displayed on the host computer.

[0098] 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.

[0099] Specifically, the clock generation unit generates a standard clock signal, providing a high-precision clock source for the normal operation of the module and signal generation; the DDS signal generation unit generates sweep frequency signals of different lengths according to different segments of the calibration signal period. The longer the period, the longer the sweep frequency time, and vice versa.

[0100] The programmable multi-channel switching module includes three programmable multi-channel switching units, two of which are connected to the analog front end in the multi-channel gain band calibration module respectively, and then connected to the long-distance transmission module, and the other switching unit is directly connected to the long-distance transmission module.

[0101] Specifically, when the programmable multi-channel switching unit is connected to the analog front end, the calibration signal needs to be pre-processed by filtering and amplification in the analog front end, and then transmitted to the multi-channel acquisition module via 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 via the long-distance transmission module.

[0102] In this embodiment, two magnetic sensors and a calibration sequence generation module are respectively connected to the switching unit 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, the two programmable multi-channel switching units in the programmable multi-channel switching module are respectively connected to the two analog front ends in the multi-channel gain to be calibrated module, and the signals are input into the analog front ends for pre-processing such as 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 signals to the multi-channel data acquisition module, which conditions each signal and performs data acquisition under the control of the MCU control and processing module. Finally, the MCU control and processing module performs signal analysis on the sampled data input by the multi-channel data acquisition module, obtains the gain characteristic curve of the circuit, and displays it on the host computer.

[0103] Figure 4 FIG is a schematic diagram of a calibration signal sequence generating module according to an embodiment of the present invention. Figure 4 As shown, the calibration signal sequence generation module includes a clock generation unit and a DDS signal generation unit. The clock generation unit generates the system clock required for the operation of the DDS signal generation unit. The accuracy of the clock signal generated by the clock generation unit will greatly 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 is required 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, thereby obtaining a cleaner clock signal for use by the DDS signal generation unit.

[0104] Continue to refer 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 will affect 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, and writes the corresponding control word into the DDS signal generation unit according to the frequency, waveform and working mode required by the user. Then the DDS signal generation unit starts working according to the written parameters and outputs the corresponding signal. The Cap end 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 to filter out the high-frequency noise contained in the signal, thereby ensuring that the signal is more stable and clean.

[0105] Figure 5 Schematic diagram of a program-controlled multi-channel switching module according to an embodiment of the present invention. Figure 5As shown, the programmable multi-channel switching module includes three programmable channel switching units, each of which includes a transistor control unit and a channel selection unit. The channel selection unit is used to set the connection between the analog front end of the gain calibration module and the magnetic sensor and calibration sequence generation module. The transistor control unit mainly controls the power supply of the channel selection unit, changing the connection relationship between the analog front end of the gain calibration module, the magnetic sensor, and the calibration sequence generation module by whether or not the channel selection unit is powered.

[0106] The transistor control unit is connected to the MCU control and processing module. High and low-level input signals control the conduction of the transistors, thereby controlling the connectivity of the channel selection unit. The channel selection unit is connected to the magnetic sensor, the calibration signal sequence generation module, and the multi-channel gain calibration module, respectively. It selects the connection between the multi-channel gain calibration module and the magnetic sensor or calibration signal sequence generation module. The long-distance transmission module connects the multi-channel gain calibration module to the multi-channel data acquisition module. The long-distance transmission module can reach tens or even hundreds of meters in length and uses a shielded twisted-pair cable for differential signal transmission.

[0107] Specifically, taking the programmable channel switching unit 1 as an example, Vcc is the power port, one end of which is connected to the power supply, and the other end is electrically connected to the collector of the transistor Q1 in the transistor 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.

[0108] It should be noted that the signal relay selected by the channel selection unit is dual-channel. In this embodiment, a dual-channel parallel structure is adopted, which can reduce the impedance to half of that of a single-channel structure, greatly reducing the energy loss during signal transmission.

[0109] Continue to refer Figure 5 Taking programmable channel switching unit 1 as an example, transistor Q1 should be an NPN transistor. The base of the transistor is electrically connected to the MCU control and processing module via first resistor R1. First resistor R1 limits current, preventing excessive signal current in the base path from causing transistor breakdown. Second resistor R2 is a pull-down resistor. One end of second resistor R2 is electrically connected to the MCU control and processing module, and the other end of second resistor R2 is electrically connected to the emitter of transistor Q1. This ensures that transistor Q1 is in the off state when the MCU control and processing module is not operating, preventing malfunctions such as transistor Q1 turning on due to noise or interference signals.

[0110] Figure 6 Schematic diagram of a multi-channel data acquisition module according to an embodiment of the present invention. Figure 6As 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.

[0111] 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 from high-precision, low-temperature drift precision resistors, one end of the eighth resistor R8 and the ninth resistor R9 are 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 Select high-precision, low-temperature drift precision resistors, the seventh resistor R7 and the tenth resistor R 10 One end of the eighth resistor R8 and the ninth resistor R9 are electrically 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 of the signal adjustment is set to:

[0112]

[0113]

[0114] 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.

[0115] Specifically, the programmable multi-channel switching unit in the programmable multi-channel switching module is electrically connected to the multi-channel gain calibration module through the long-distance transmission module on two channels; and is directly electrically connected to the multi-channel data acquisition module on one channel through the long-distance transmission module.

[0116] Continue to refer Figure 6 Taking signal sampling unit 1 as an example, the sampling chip selects a high-bit and high-sampling-rate chip with a differential input structure, which ensures high time resolution while ensuring the efficiency and convenience of the MCU control and processing module in organizing and transmitting data from each channel.

[0117] Figure 7 FIG. 1 is a flow chart of a signal amplitude extraction method of a signal analysis unit according to an embodiment of the present invention. Figure 7As 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, completing the data separation of each channel, and obtaining the sampling data corresponding to each channel; for the sampling data of each channel, based on the same source clock, the data of each channel are simultaneously stored to meet the subsequent processing requirements; performing short-time Fourier transform on the data, and solving the power spectrum density distribution result of the swept frequency signal; calculating the amplitude of the swept frequency signal in each swept frequency time period, obtaining the intensity of the swept frequency signal, and obtaining the amplitudes of three channel signals, two of which 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 by frequency traversal; finally, performing linear interpolation on the obtained result with the required specific frequency resolution to obtain the gain change curve in the entire detection frequency band of the detection system. The real circuit gain of the detection system in the entire frequency band can be obtained remotely online anytime and anywhere, providing important support for the subsequent inversion calculation of the real strength of the received signal and significantly improving the accuracy of the inversion calculation.

[0118] It should be noted that when storing the sampled data of each channel, it must be based on the same 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 actual sampling time, thereby ensuring the authenticity of the final gain result.

[0119] In summary, the present invention designs a remote online automatic calibration method and system for 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 signal. The MCU module uses digital signals to calculate the gain parameters of the target frequency point, and generates the gain change curve within the entire passband through the interpolation method, and finally transmits the result to the host computer for display. The present invention can realize remote online automatic calibration anytime and anywhere according to demand, accurately provide the actual circuit gain of each frequency point, effectively improve the problem of low accuracy of received signal strength restoration, and provide reliable protection for the detection task of extremely low frequency / very low frequency bands.

[0120] The innovation of this invention lies primarily in its ability to perform remote online calibration, eliminating the need for external instruments and equipment. It can perform multi-channel, high-precision calibration in real time in an unattended environment, greatly improving calibration efficiency and flexibility. Furthermore, by comparing the calibration reference signal with the target signal and combining it with an interpolation algorithm, the system generates a high-resolution gain change curve, significantly improving the accuracy of restoring the true signal strength. These features make it particularly suitable for detection missions 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 ionospheric D layer.

[0121] Furthermore, this invention can be further improved to enhance its performance. For example, the system's stability and adaptability in extreme environments can be enhanced; frequency coverage can be expanded to meet the needs of more complex application scenarios through hardware and algorithm optimization; intelligent technology can be introduced to improve the dynamic prediction and compensation capabilities for gain changes; and modular design can enable flexible system upgrades. These improvements will further expand the application scope of this invention and lay a solid foundation for the development of extremely low frequency (ELF) and very low frequency (VLF) detection technology.

[0122] The present invention also provides a very low frequency detection system analog front-end gain automatic calibration device. The very low frequency detection system analog front-end gain automatic calibration device provided by the present invention is described below. The very low frequency detection system analog front-end gain automatic calibration device described below and the very low frequency detection system analog front-end gain automatic calibration method described above can be referenced to each other. Figure 8 This is a structural block diagram of the automatic calibration device for analog front-end gain of a very low frequency detection system provided by the present invention. Figure 8 As shown, the device includes:

[0123] A generating module 801 is configured to generate a calibration signal sequence based on a total calibration time limit of an analog front-end circuit and a frequency sweep signal period;

[0124] The acquisition module 802 is used to acquire data of the calibration signal sequence to obtain sampled data;

[0125] The analysis module 803 is used to perform signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point and determine the curve of the gain of each frequency sweep signal versus frequency;

[0126] The calibration module 804 is configured to perform linear interpolation based on the circuit gain at each frequency sweep point to obtain a gain variation curve corresponding to the analog front-end circuit.

[0127] When the present device is in use, first, the generation module 801 generates a specific calibration signal sequence based on the total calibration time 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. The analysis module 803 then performs signal analysis on the sampled data to obtain the circuit gain of each sweep point, and determines the curve of the gain change of each sweep signal with frequency. Finally, the calibration module 804 obtains the gain change curve of a specific frequency resolution within the working frequency band through interpolation of a specific frequency step. In the above process, the signal extraction, storage and amplitude analysis can be completed, the system gain at a specific sweep point can be solved, and the in-band full-band gain change curve of a specific frequency resolution can be obtained by combining the interpolation method. The present device can be automatically calibrated online anytime and anywhere according to demand, and accurately obtain the actual circuit gain of the detection system at each frequency point, thereby significantly improving the restoration accuracy of the true strength of the received signal and solving the problem of insufficient accuracy in the prior art.

[0128] Figure 9 An example of a physical structure diagram of an electronic device is shown below. Figure 9 As shown, the electronic device may include: a processor 901, a communication interface 902, a memory 903, and a communication bus 904, wherein the processor 901, the communication interface 902, and the memory 903 communicate with each other via the communication bus 904. The processor 901 may call the logic instructions in the memory 903 to execute a method for automatically calibrating the gain of an analog front-end of a very low frequency detection system, the method comprising:

[0129] Generate a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the frequency sweep signal period;

[0130] Performing data acquisition on the calibration signal sequence to obtain sampling data;

[0131] Perform signal analysis on the sampled data to obtain the circuit gain at each frequency sweep point, and determine the curve of each frequency sweep signal gain versus frequency;

[0132] 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.

[0133] Furthermore, the logic instructions in the aforementioned memory 903 can be implemented as software functional units and, when sold or used as independent products, can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product, stored in a storage medium, includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the various embodiments of the method of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a mobile hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0134] On the other hand, the present invention further provides a computer program product, which 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 perform the automatic calibration method for the analog front-end gain of a very low frequency detection system provided by the above methods, which includes:

[0135] Generate a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the frequency sweep signal period;

[0136] Performing data acquisition on the calibration signal sequence to obtain sampling data;

[0137] Perform signal analysis on the sampled data to obtain the circuit gain at each frequency sweep point, and determine the curve of each frequency sweep signal gain versus frequency;

[0138] 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.

[0139] In another aspect, the present invention further provides a non-transitory computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for automatically calibrating the analog front-end gain of a very low frequency detection system provided by the above methods is implemented. The method includes:

[0140] Generate a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the frequency sweep signal period;

[0141] Performing data acquisition on the calibration signal sequence to obtain sampling data;

[0142] Perform signal analysis on the sampled data to obtain the circuit gain at each frequency sweep point, and determine the curve of each frequency sweep signal gain versus frequency;

[0143] 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.

[0144] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0145] Through the above description of the embodiments, those skilled in the art will clearly understand that each embodiment can be implemented using software plus a necessary general-purpose hardware platform, or of course, hardware. Based on this understanding, the essence of the above technical solution, or the portion 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, a magnetic disk, or an optical disk, and includes a number of instructions for causing a computer device (such as a personal computer, server, or network device) to execute the methods described in each embodiment or certain portions of the embodiments.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for automatic calibration of analog front-end gain of a very low frequency detection system, characterized in that: include: Generate a calibration signal sequence based on the total calibration time limit of the analog front-end circuit and the frequency sweep signal period; Performing data acquisition on the calibration signal sequence to obtain sampling data; Performing signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point, and determining a curve of the gain of each frequency sweep signal versus frequency; Performing linear interpolation based on the circuit gain of each of the frequency sweep points to obtain a gain change curve corresponding to the analog front-end circuit; Performing signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point and determining the curve of each frequency sweep signal gain versus frequency, including: Performing signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range; Based on the power spectrum density distribution diagram, performing energy integration on each of the frequency sweeping points to obtain the signal strength of each of the frequency sweeping points; Based on the signal strength of each of the frequency sweep points, a circuit gain corresponding to the frequency sweep point is obtained; Based on the circuit gain corresponding to each of the frequency sweep points, determining a curve of each frequency sweep signal gain varying with frequency; Perform signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range, including: Extracting and separating the sampled data in different channels according to the arrangement order at the time of sampling; Simultaneously storing the extracted and separated sampling data; The sampling data of each channel is subjected to FIR filtering and short-time Fourier transform to obtain the power spectrum density distribution diagram of the signal within the entire frequency sweep range.

2. The method for automatic calibration of analog front-end gain of a very low frequency detection system according to claim 1, characterized in that: Based on the total calibration time limit of the analog front-end circuit and the sweep signal period, a calibration signal sequence is generated, including: The frequency sweep range is divided into several frequency bands in combination with the total calibration time limit of the analog front-end circuit and the frequency sweep signal period; For each of the frequency bands, setting corresponding frequency sweep parameters; A control word corresponding to the frequency sweep parameter of each frequency band is acquired, and the calibration signal sequence is generated based on the control word.

3. The method for automatic calibration of analog front-end gain of a very low frequency detection system according to claim 1, characterized in that: Performing data acquisition on the calibration signal sequence to obtain sampled data includes: performing amplitude adjustment on the calibration signal sequence; The calibration signal sequence after amplitude adjustment is sampled to obtain the sampled data.

4. The method for automatic calibration of analog front-end gain of a very low frequency detection system according to claim 1, characterized in that: Based on the power spectrum density distribution diagram, energy integration is performed on each of the frequency sweep points to obtain the signal strength of each of the frequency sweep points, including: For each of the frequency sweep points, calibration signals of several channels are subjected to signal conditioning to obtain a first signal strength, and calibration signals of the remaining channels are subjected to gain calibration and signal conditioning to obtain a second signal strength.

5. The method for automatic calibration of analog front-end gain of a very low frequency detection system according to claim 4, characterized in that: Obtaining a circuit gain corresponding to each of the frequency sweep points based on the signal strength of the frequency sweep point includes: The circuit gain corresponding to the frequency sweep point is determined according to the ratio of the second signal strength to the first signal strength at the frequency sweep point.

6. The method for automatic gain calibration of an analog front-end of a very low frequency detection system according to claim 1, wherein: Based on the circuit gain of each of the frequency sweep points, linear interpolation is performed to obtain a gain change curve corresponding to the analog front-end circuit, including: For each of the sweep frequency points within the entire sweep frequency range, the frequency is linearly interpolated according to a preset step size to obtain a gain variation characteristic corresponding to the analog front-end circuit when the frequency resolution is the preset step size; The gain variation curve is generated based on the gain variation characteristic of each of the frequency sweep points.

7. A very low frequency detection system analog front-end gain automatic calibration system, characterized in that: include: A magnetic sensor is used 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 generating module, used for generating a calibration signal sequence; a programmable multi-channel switching module, configured to transmit the electrical signal output by the magnetic sensor or the calibration signal output by the calibration signal sequence generating module; A multi-channel gain calibration module, used for pre-processing the calibration signal transmitted by the program-controlled multi-channel switching module; A long-distance transmission module, used for transmitting the analog signal output by the multi-channel gain calibration module to a subsequent processing module over a long distance; A multi-channel acquisition module, used to condition the analog signal transmitted by the long-distance transmission module and complete data acquisition; MCU control and processing module, used to complete the functional control of each module, as well as data transmission and processing; Host computer, used to display the gain calibration results; Perform signal analysis on the sampled data to obtain the circuit gain at each sweep point and determine the curve of each sweep signal gain versus frequency, including: Performing signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range; Based on the power spectrum density distribution diagram, performing energy integration on each of the frequency sweeping points to obtain the signal strength of each of the frequency sweeping points; Based on the signal strength of each of the frequency sweep points, a circuit gain corresponding to the frequency sweep point is obtained; Based on the circuit gain corresponding to each of the frequency sweep points, determining a curve of each frequency sweep signal gain varying with frequency; Perform signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range, including: Extracting and separating the sampled data in different channels according to the arrangement order at the time of sampling; Simultaneously storing the extracted and separated sampling data; The sampling data of each channel is subjected to FIR filtering and short-time Fourier transform to obtain the power spectrum density distribution diagram of the signal within the entire frequency sweep range.

8. A very low frequency detection system analog front-end gain automatic calibration device, characterized in that: include: A generation module, configured to generate a calibration signal sequence based on a total calibration time limit of an analog front-end circuit and a frequency sweep signal period; An acquisition module, configured to acquire data from the calibration signal sequence to obtain sampled data; An analysis module is used to perform signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point and determine the curve of the gain of each frequency sweep signal as a function of frequency; a calibration module, configured to perform linear interpolation based on the circuit gain of each of the frequency sweep points to obtain a gain change curve corresponding to the analog front-end circuit; Performing signal analysis on the sampled data to obtain the circuit gain of each frequency sweep point and determining the curve of each frequency sweep signal gain versus frequency, including: Performing signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range; Based on the power spectrum density distribution diagram, performing energy integration on each of the frequency sweeping points to obtain the signal strength of each of the frequency sweeping points; Based on the signal strength of each of the frequency sweep points, a circuit gain corresponding to the frequency sweep point is obtained; Based on the circuit gain corresponding to each of the frequency sweep points, determining a curve of each frequency sweep signal gain varying with frequency; Perform signal analysis on the sampled data to obtain a power spectrum density distribution diagram of the signal within the entire frequency sweep range, including: Extracting and separating the sampled data in different channels according to the arrangement order at the time of sampling; Simultaneously storing the extracted and separated sampling data; The sampling data of each channel is subjected to FIR filtering and short-time Fourier transform to obtain the power spectrum density distribution diagram of the signal within the entire frequency sweep range.

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