A sonar buoy preprocessing gain automatic control system and adjustment method

Abstract

The present invention provides a sonar buoy preprocessing gain automatic control system and adjustment method, which adopts a high impedance differential amplifier to couple weak sonar signals, divides the gain amplification into three stages: weak fixed amplification, variable gain, and fixed amplification, transforms the effective value of the output signal in the variable gain stage into feedback information, and completes automatic and accurate control of the gain in the variable gain stage, so as to achieve the purpose of accurate amplification of the wide dynamic range of the sonar signal. The weak signal received by the buoy is amplified and filtered, and finally a V-level signal is output. The present invention can stably amplify the sonar signal with a wide dynamic range, and the amplification gain can be automatically controlled without manual intervention. According to the actual use background, the accurate amplification and attenuation control of the sonar signal can be realized, and the sonar product design that has high integration, stable and reliable performance, and is easier to meet the needs of multi-channel sonar signal amplification.

Description

Technical Field

[0001] The present invention relates to the field of signal processing engineering, and is used to solve the problem of automatic control of the gain of a wide dynamic range sonar signal under the interference of ocean background noise and reverberation, and is particularly used for a gain control method of a wide dynamic range sonar echo signal in an active or passive working mode of the sonar to achieve accurate detection of a target. Background Art

[0002] The long-distance detection performance of aerial suspended sonar, sonar buoys and other related products for underwater targets heavily relies on the amplification and filtering technology of wide dynamic range sonar signals. Based on the characteristics of ocean channels and the characteristics of sonar long-range detection, the acoustic signal of the detection echo presents the characteristics of low signal-to-noise ratio, short and severe pulse broadening, reverberation interference, and large signal dynamic range. In response to the needs of long-range detection of sonar systems, the present invention refers to a sonar buoy preprocessing gain automatic control method that divides the gain control into three stages: fixed gain of μV to MV level, automatic variable gain of MV to V level, and fixed gain of V level, and converts the effective value of the output signal in the intermediate stage into feedback information. In the intermediate stage of MV to V level, accurate control of the gain is achieved to achieve the purpose of automatic control of the preprocessing gain. The above functions can adjust the working frequency band and gain range of the amplification system according to the actual needs of the sonar system, and have good versatility.

[0003] There are three main wide dynamic range sonar signal amplification technologies in the field of underwater acoustics in China. The first is a technology based on analog voltage controlled gain. This method uses a voltage-controlled gain amplifier as the core and realizes linear gain control from -40dB to +40dB. Luo Youliang et al. also introduced a similar scheme in the article "Large Dynamic Range AGC Circuit Design Based on VCA810" (Electronic Engineering Design, 2016). The characteristics of this type of technology are that the dynamic range of amplification and attenuation is the same, and a stable, high-precision, low-noise analog voltage control signal is required. For the needs of long-range detection of sonar systems, this technology does not give full play to its ability to amplify weak signals. The single-stage amplification dynamic range is only 40dB. If a larger amplification range is required, multi-stage cascade is required, and high-precision voltage control signals require more complex circuit design to achieve the desired effect.

[0004] The second is a technology based on digital controlled attenuation. This method takes a digital controlled attenuator or DA converter as the core, takes the acoustic signal as the analog reference, and uses the DA conversion method to determine the attenuation of the analog acoustic signal through the provided digital code. Wang Feng et al. also introduced a similar scheme in the article "Research on High-precision Sonar Signal Preprocessing System" (Data Acquisition and Processing, 2002). The relevant technology has been applied to the preprocessing system of a certain type of aviation dipping sonar in the mid-1990s. The characteristic of this type of technology is that the acoustic signal is amplified first, and then the signal is attenuated step by step through the attenuator. This method can achieve stable control for long pulse signals and continuous signals, but it is easy to have excessive amplification, short pulse signal limiting, attenuation code jump and other phenomena for short pulse signals.

[0005] The third is the gain control technology based on threshold estimation. This method counts the number of times the received signal amplitude crosses the threshold line within a period of time, and adjusts the amplification gain based on the statistical results. Li Heng et al. conducted an in-depth study and detailed description of this technology in the article "Automatic Gain Control of Underwater Acoustic Communication Receivers Based on Threshold Estimation" (Journal of PLA University of Science and Technology (Natural Science Edition), 2015). This technology requires manual determination of the statistical time and threshold standard, and has weak discrimination ability for short pulse echo signals with low signal-to-noise ratio. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a sonar buoy preprocessing gain automatic control system and adjustment method. In order to meet the requirements of making the amplification dynamic range greater than the attenuation dynamic range during sonar operation, avoiding the loss of phase information by amplification limiting, and realizing automatic control of amplification gain without manual intervention, the existing sonar signal amplification control technology has deficiencies in engineering implementation. The purpose of the present invention is to use a high-impedance differential amplifier to couple weak sonar signals, divide the gain amplification into three stages: weak fixed amplification, variable gain, and fixed amplification, transform the effective value of the output signal of the variable gain stage into feedback information, and complete automatic and precise control of the gain in the variable gain stage, so as to achieve the purpose of precise amplification of the sonar signal with a wide dynamic range.

[0007] The technical solution adopted by the present invention to solve the technical problem comprises the following steps:

[0008] A sonar buoy preprocessing gain automatic control system, wherein a differential amplifier is directly connected to a hydrophone, the differential amplifier performs a first pre-amplification on a signal coupled to the hydrophone, the pre-amplified signal passes through a first fixed amplifier circuit for a second fixed gain amplification, and then undergoes high-pass filtering, the high-pass filtered signal passes through a two-stage cascaded variable gain amplifier circuit for a third variable gain amplification; the output signal of the variable gain amplifier circuit passes through a band-pass filter, enters a second fixed amplifier circuit for a fourth fixed gain amplification, and the amplified signal passes through a low-pass filter before being output;

[0009] Among them, the variable gain amplifier circuit outputs a signal as the feedback signal. The feedback signal converts the AC signal into a DC signal through a root mean square DC converter, and then the single-chip microcomputer collects the DC signal and generates a gain control code to control the resistance value of the feedback resistor in the variable gain amplifier circuit.

[0010] Select a differential amplifier according to the hydrophone. The output impedance of the hydrophone is much smaller than the input impedance of the differential amplifier. The physical connection distance between the differential amplifier and the hydrophone should be as short as possible, with a physical distance of 0.25 m - 0.5 m. Determine that the gain of the second fixed amplification is 1 - 10 times, and the cut-off frequency of the high-pass filter is 15 kHz - 20 kHz.

[0011] In the variable gain amplifier circuit, a digital potentiometer is used as the feedback resistor and is combined with a low-noise operational amplifier to form an inverting amplifier circuit. The input resistor is connected to the inverting input terminal of the low-noise operational amplifier. Two groups of inverting amplifier circuits are cascaded, and the two-stage cascade realizes the expansion of the dynamic range.

[0012] The band-pass filter circuit uses an analog filter. Adjust the band-pass filter parameters according to the application requirements, perform the fourth fixed gain amplification on the signal to compensate for the signal attenuation in the circuit. The amplification factor of the fourth amplification in the second fixed amplification circuit is 1 - 10 times, and the signal is output after low-pass filtering.

[0013] The feedback signal is converted into a DC signal through a root mean square DC converter. The single-chip microcomputer collects this DC signal, combines it with the gain of the variable gain amplifier circuit, generates the configuration parameters required for the digital potentiometer, and completes the automatic gain control of signal amplification. The single-chip microcomputer provides an interface for manual gain control, enabling the sonar operator to adjust the amplification amount of the variable gain according to the actual listening effect.

[0014] Digital potentiometer R C is a sliding rheostat. The digital potentiometer R C is controlled by the program instructions sent by the single-chip microcomputer for the gear position. It is the feedback resistor of the variable gain amplifier circuit and forms an inverting amplifier with the input resistor R of the variable gain amplifier circuit. The amplification factor of the inverting amplifier is expressed as G = -R C / R, and the negative sign indicates that the phase of the signal is flipped by 180 degrees. By adjusting R C , the amplification or attenuation of the electrical signal is achieved. When R C > R, |G| > 1, and the electrical signal is amplified; when R C < R, |G| < 1, and the electrical signal is attenuated.

[0015] The digital potentiometer R CThe AD5293 chip is used. The resistance value is 100kΩ when the full gear is in full gear. There are 1024 gears that can be adjusted. The resistance value of each gear is 97.65Ω. The input resistance R is 1kΩ. By adjusting the 1024 gears, the gain of the electrical signal can be adjusted step by step. According to G=-R C / R obtains an amplification factor of 0.09765 times for each level, with a total of 1024 levels. When the resistance of the digital potentiometer is less than 1kΩ, that is, in levels 1 to 10, the circuit realizes the attenuation function. When the resistance of the digital potentiometer is greater than 1kΩ, that is, in levels 11 to 1024, the circuit realizes the amplification function.

[0016] A method for adjusting a sonar buoy preprocessing gain automatic control system, the specific steps are:

[0017] The AC signal is converted into a DC signal through a root mean square DC converter and sent to the single-chip microcomputer. The level of the DC signal is compared with the reference level in the single-chip microcomputer to determine the new amplification factor, and the amplification factor is sent to the digital potentiometer in the form of program instructions to adjust the amplification of the original AC signal. The sampling and judgment process uses a DC signal to effectively reduce the interference caused by other signals and the original AC signal of the program instruction; the adjustment steps are:

[0018] 1) After the AC signal is converted from digital to analog, a DC level s is obtained, and it is determined whether the DC level s is greater than a first threshold s1, where s1 is 5264. If s is greater than s1, the program instruction G of the microcontroller controlling the amplification factor is multiplied by 0.707 to obtain a new G, and the new G is input into the digital potentiometer; otherwise, proceed to step 2);

[0019] 2) Determine whether the DC level s is greater than a second threshold s2, where s2 is 0. If s is greater than s2, the program instruction G for controlling the amplification factor of the single-chip microcomputer is directly input into the digital potentiometer; otherwise, proceed to step 3);

[0020] 3) The program instruction G of the microcontroller controlling the magnification is multiplied by the third threshold value s3 and then divided by s according to the formula G to obtain a new G, where s3 = 1974-3212, and then the new G is input into the digital potentiometer;

[0021] The beneficial effect of the present invention is to amplify and filter the weak signal (generally at the μV level) received by the buoy, and finally output a V-level signal through multi-stage amplification and filtering and a controllable amplification module constructed by a single-chip microcomputer and a digital potentiometer. Since the present invention adopts AC to DC conversion for sampling and judgment, the anti-interference ability is stronger than the effect of directly using AC signals. The sonar signal with a wide dynamic range can be stably amplified, and the amplification gain can be automatically controlled without human intervention. According to the actual use background, the precise amplification and attenuation control of the sonar signal can be achieved. The circuit designed based on the present invention has high integration, stable and reliable performance, and is easier to design sonar products that meet the needs of multi-channel sonar signal amplification. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram of a sonar buoy preprocessing gain automatic control system.

[0023] Figure 2 This is the schematic diagram of the first preamplification;

[0024] Figure 3 This is the schematic diagram of the second fixed amplification high-pass filter;

[0025] Figure 4 This is the third variable gain amplification principle diagram;

[0026] Figure 5 This is the principle diagram of bandpass filtering;

[0027] Figure 6 This is the fourth fixed amplification low-pass filter principle diagram;

[0028] Figure 7 This is the gain control principle diagram.

[0029] Figure 8 Flow chart of adjusting the amplification of the digital potentiometer of the present invention. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0031] In the present invention, in stage 1, a high impedance differential amplifier is used to couple the hydrophone signal for low noise fixed amplification, and the μV signal is amplified to the mV level; in stage 2, a low noise operational amplifier and a digitally controlled potentiometer are used to realize a gain controllable design, and the signal is controlled within the mV to V level; in stage 3, a fixed gain amplification is performed, and the effective value of the output signal is calculated to generate a gain control code, and the gain control code is used to control the precise gain of the circuit in stage 2. The design has a simple structure, the system parameters are easy to adjust, the scheme is easy to implement, it has strong practicality, and is easy to promote and use.

[0032] A sonar buoy preprocessing gain automatic control system, such as Figure 1As shown, the differential amplifier is directly connected to the hydrophone, and the differential amplifier performs the first pre-amplification on the signal coupled by the hydrophone. The pre-amplified signal is amplified by the first fixed amplifier circuit for the second fixed gain, and then high-pass filtered. The signal after high-pass filtering is amplified by the two-stage cascade variable gain amplifier circuit for the third variable gain amplification. The output signal of the variable gain amplifier circuit is band-pass filtered and then enters the second fixed amplifier circuit for the fourth fixed gain amplification. The amplified signal is low-pass filtered and then output.

[0033] Among them, the variable gain amplifier circuit outputs a signal as a feedback signal. The feedback signal converts the AC signal into a DC signal through a root mean square DC converter, and then the DC signal is collected by the microcontroller to generate a gain control code. The gain control code is used to control the resistance value of the feedback resistor in the variable gain amplifier circuit.

[0034] Select a differential amplifier based on the hydrophone. The output impedance of the hydrophone is much smaller than the input impedance of the differential amplifier. The physical connection distance between the differential amplifier and the hydrophone is as short as possible, which is 0.25m-0.5m. The gain of the second fixed amplification is determined to be 1-10 times, and the cutoff frequency of the high-pass filter is 15kHz-20kHz.

[0035] In the variable gain amplifier circuit, a digitally controlled potentiometer is used as a feedback resistor to form an inverting amplifier circuit with a low-noise operational amplifier, an input resistor is connected to the input inverting terminal of the low-noise operational amplifier, two sets of inverting amplifier circuits are cascaded, and the two-stage cascade realizes the expansion of the dynamic range.

[0036] The bandpass filter circuit adopts an analog filter, adjusts the bandpass filter parameters according to application requirements, performs a fourth fixed gain amplification on the signal, compensates for the signal attenuation of the circuit, the fourth amplification in the second fixed amplification circuit is 1-10 times, and the signal is output after low-pass filtering.

[0037] The feedback signal is converted into a DC signal through a root mean square DC converter. The single chip microcomputer collects the DC signal and generates the configuration parameters required by the digitally controlled potentiometer in combination with the gain of the variable gain amplifier circuit to complete the automatic gain control of the signal amplification. The single chip microcomputer provides an interface for manual gain control, so that the sonar operator can adjust the variable gain amplification according to the actual listening effect.

[0038] Digital potentiometer R C For sliding rheostat, digital potentiometer R C The gear position is controlled by the program instruction sent by the single chip microcomputer. It is the feedback resistor of the variable gain amplifier circuit, and forms an inverting amplifier with the input resistor R of the variable gain amplifier circuit. The amplification factor of the inverting amplifier is expressed as G = -R C / R, the negative sign indicates that the phase of the signal is flipped 180 degrees.C , to achieve amplification or attenuation of the electrical signal. When R C > R, |G| > 1, and the electrical signal is amplified; when R C < R, |G| < 1, and the electrical signal is attenuated.

[0039] The digital potentiometer R C employs the AD5293 chip, with a resistance value of 100 kΩ at full scale. There are 1024 adjustable positions in total, and the resistance value of each position is 97.65 Ω. The input resistance R is 1 kΩ. Then, by adjusting the 1024 positions, the gain of the electrical signal is adjusted step by step. According to G = -R C / R, the amplification factor of each stage is 0.09765 times, with a total of 1024 stages. When the resistance of the digital potentiometer is less than 1 kΩ, that is, in the range of 1 - 10 positions, the circuit realizes the attenuation function. When the resistance of the digital potentiometer is greater than 1 kΩ, that is, in the range of 11 - 1024 positions, the circuit realizes the amplification function.

[0040] The AC signal is converted into a DC signal through a root - mean - square DC converter and sent to the single - chip microcomputer. Inside the single - chip microcomputer, the level of this DC signal is compared with the reference level to determine the new amplification factor, and the amplification factor is sent to the digital potentiometer in the form of program instructions to adjust the amplification amount of the original AC signal. The sampling and judgment process uses DC signals, effectively reducing the interference caused by other signals and program instructions to the original AC signal; as Figure 8 shown, the adjustment steps are as follows:

[0041] 1) After the AC signal undergoes digital - to - analog conversion, a DC level s is obtained. Determine whether the DC level s is greater than the first threshold s1, where s1 is set to 5264. If s is greater than s1, multiply the program instruction G for controlling the amplification factor of the single - chip microcomputer by 0.707 to obtain the new G, and input the new G into the digital potentiometer; otherwise, proceed to step 2)

[0042] 2) Determine whether the DC level s is greater than the second threshold s2. If s is greater than s2, where s2 is set to 0, directly input the program instruction G for controlling the amplification factor of the single - chip microcomputer into the digital potentiometer; otherwise, proceed to step 3);

[0043] 3) Multiply the program instruction G for controlling the amplification factor of the single - chip microcomputer by the third threshold s3 and then divide by s according to the formula G to obtain the new G, where s3 = 1974 - 3212, and then input the new G into the digital potentiometer;

[0044] The calculation formula for controlling the digital potentiometer is R C = G×R, where R is set to 97.65.

[0045] The embodiments are as follows:

[0046] The system is powered by ±9-±15V DC, the hydrophone output signal range is 10-100μV, the amplification dynamic range is greater than 80dB, the total gain is greater than 110dB, and the power consumption is less than 1 watt.

[0047] The specific implementation of this example is as follows:

[0048] (a) Select a suitable high-precision, low-noise differential amplifier based on the output impedance of the hydrophone used, so that the output impedance of the hydrophone is much smaller than the input impedance of the amplifier. The two ends of the amplifier are directly connected to the transducer output, and the physical connection is as short as possible. The amplification gain is 40dB. Figure 2 shown.

[0049] (b) According to the requirements of the usage scenario, determine the multiple of the second fixed gain amplification, and use the UAF42 analog filter to construct a second-order high-pass filter. Figure 3 As shown, the amplifier INA128 can be selected, the resistor R1 determines the amplification factor, and the resistors Rg, Rq, and Rf determine the cutoff frequency of the UAF42 second-order high-pass.

[0050] (c) Figure 4 As shown, AD797 can be used to construct an inverting amplifier, the digitally controlled potentiometer AD5293 is used as the feedback resistor, and the input resistors R4 and R5 are 1KΩ high-precision resistors. A dynamic range of 80dB can be achieved through a two-stage cascade.

[0051] (d) Two UAF42 chips are cascaded to construct a fourth-order bandpass filter. The required filter center frequency and filter bandwidth can be achieved through the configuration of resistors Rg, Rq, and Rf according to the needs of the usage scenario. Figure 5 shown.

[0052] (e) If Figure 6 As shown, the amplification of the system is compensated by fixed gain amplification, and resistors R6 and R7 determine the amplification. UAF42 is used to construct a second-order low-pass filter.

[0053] (f) Figure 4 The output signal is introduced as a feedback signal Figure 7 After the high-precision RMS DC converter, the microcontroller combines the converted effective value with the gain control to generate a control code to control the resistance value of the digitally controlled potentiometer AD5293. The control code is output to Figure 4 AD5293 control end.

[0054] This example amplifies the weak signal four times, and the gain distribution can be flexibly adjusted according to the scene requirements. The first preamplification gain range is 30-40dB, the second fixed gain amplification can be selected from 1 to 10 times according to specific needs, the third variable gain amplification dynamic range is 80dB, the amplitude adjustment accuracy is 0.1 times / level, and the fourth fixed gain amplification is set at 1-10 times.

[0055] The advantages of the present invention are:

[0056] 1) The dynamic range can be designed according to user needs, and the amplification and attenuation range is not limited by the existing programmable gain control chip.

[0057] 2) High control accuracy;

[0058] 3) AC to DC sampling and statistical calculation minimize the interference of pulse interference and power frequency interference on the control effect, and have strong anti-interference ability.

Claims

1. A sonar buoy preprocessing gain automatic control system, characterized in that: The sonar buoy preprocessing gain automatic control system, the differential amplifier is directly connected to the hydrophone, the differential amplifier performs a first preamplification on the signal coupled to the hydrophone, the preamplified signal passes through a first fixed amplifier circuit to perform a second fixed gain amplification, and then performs a high-pass filter, and the high-pass filtered signal passes through a two-stage cascaded variable gain amplifier circuit to achieve a third variable gain amplification; The output signal of the variable gain amplifier circuit is subjected to bandpass filtering, and then enters the second fixed amplifier circuit for a fourth fixed gain amplification, and the amplified signal is subjected to low-pass filtering before being output; Among them, the variable gain amplifier circuit outputs a signal as a feedback signal. The feedback signal converts the AC signal into a DC signal through a root mean square DC converter, and then the DC signal is collected by the microcontroller to generate a gain control code. The gain control code is used to control the resistance value of the feedback resistor in the variable gain amplifier circuit.

2. The sonobuoy preprocessing gain automatic control system according to claim 1, characterized in that: A differential amplifier is selected according to the hydrophone. The output impedance of the hydrophone is much smaller than the input impedance of the differential amplifier. The physical distance between the differential amplifier and the hydrophone is 0.25m-0.5m. The gain of the second fixed amplification is determined to be 1-10 times, and the cutoff frequency of the high-pass filter is 15kHz-20kHz.

3. The sonar buoy preprocessing gain automatic control system according to claim 1, characterized in that: In the variable gain amplifier circuit, a digitally controlled potentiometer is used as a feedback resistor to form an inverting amplifier circuit with a low-noise operational amplifier, an input resistor is connected to the input inverting terminal of the low-noise operational amplifier, two sets of inverting amplifier circuits are cascaded, and the two-stage cascade realizes the expansion of the dynamic range.

4. The sonar buoy preprocessing gain automatic control system according to claim 1, characterized in that: The bandpass filter circuit adopts an analog filter, adjusts the bandpass filter parameters according to application requirements, performs a fourth fixed gain amplification on the signal, compensates for the signal attenuation of the circuit, the fourth amplification in the second fixed amplification circuit is 1-10 times, and the signal is output after low-pass filtering.

5. The sonobuoy preprocessing gain automatic control system according to claim 1, characterized in that: The feedback signal is converted into a DC signal through a root mean square DC converter. The single chip microcomputer collects the DC signal and generates the configuration parameters required by the digitally controlled potentiometer in combination with the gain of the variable gain amplifier circuit to complete the automatic gain control of the signal amplification. The single chip microcomputer provides an interface for manual gain control, so that the sonar operator can adjust the variable gain amplification according to the actual listening effect.

6. The sonobuoy preprocessing gain automatic control system according to claim 1, characterized in that: Digital potentiometer R C is a slide rheostat. The digital potentiometer R C is controlled by the program instructions sent by the single-chip microcomputer for the gear position. It is the feedback resistor of the variable gain amplifier circuit and forms an inverting amplifier with the input resistor R of the variable gain amplifier circuit. The amplification factor of the inverting amplifier is expressed as G = -R C / R. The negative sign indicates that the phase of the signal is flipped by 180 degrees. By adjusting R C , the amplification or attenuation of the electrical signal is achieved. When R C > R, |G| > 1, and the electrical signal is amplified; when R C < R, |G| < 1, and the electrical signal is attenuated.

7. The sonobuoy preprocessing gain automatic control system according to claim 6, characterized in that: The digital potentiometer R C The AD5293 chip is used. The resistance value is 100kΩ when the full gear is in full gear. There are 1024 gears that can be adjusted. The resistance value of each gear is 97.65Ω. The input resistance R is 1kΩ. By adjusting the 1024 gears, the gain of the electrical signal can be adjusted step by step. According to G=-R C / R obtains an amplification factor of 0.09765 times for each level, with a total of 1024 levels. When the resistance of the digital potentiometer is less than 1kΩ, that is, in levels 1 to 10, the circuit realizes the attenuation function. When the resistance of the digital potentiometer is greater than 1kΩ, that is, in levels 11 to 1024, the amplification function is realized.

8. A method for adjusting the sonar buoy preprocessing gain automatic control system according to claim 1, characterized in that The steps include: The AC signal is converted into a DC signal through a root mean square DC converter and sent to the single-chip microcomputer. The level of the DC signal is compared with the reference level in the single-chip microcomputer to determine the new amplification factor, and the amplification factor is sent to the digital potentiometer in the form of program instructions to adjust the amplification of the original AC signal. The sampling and judgment process uses a DC signal to effectively reduce the interference caused by other signals and the original AC signal of the program instruction; the adjustment steps are: 1) After the AC signal is converted from digital to analog, a DC level s is obtained, and it is determined whether the DC level s is greater than a first threshold s1, where s1 is 5264. If s is greater than s1, the program instruction G of the microcontroller controlling the amplification factor is multiplied by 0.707 to obtain a new G, and the new G is input into the digital potentiometer; Otherwise, go to step 2); 2) Determine whether the DC level s is greater than a second threshold s2, where s2 is 0. If s is greater than s2, the program instruction G for controlling the amplification factor of the single-chip microcomputer is directly input into the digital potentiometer; otherwise, proceed to step 3); 3) The program instruction G of the microcontroller controlling the amplification factor is multiplied by the third threshold value s3 and then divided by s according to the formula G to obtain a new G, where s3 is 1974 to 3212, and then the new G is input into the digital potentiometer.

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