High-frequency voltage sampling circuit

Abstract

The utility model discloses a high-frequency voltage sampling circuit. The high-frequency voltage sampling circuit comprises a precise rectification module, an operational amplifier module and a differential module, the input end of the precision rectification module is connected with AC voltage, and the output end is connected with the input end of the operational amplifier module. The output end of the operational amplifier module is connected with the input end of the differential module; the differential module transmits sampling signals through a pair of differential lines, and signals on the pair of differential lines are equal in amplitude but opposite in phase. Wherein the precise rectification module converts an alternating current input signal into a one-way output signal, negative feedback is used for correcting signal loss possibly caused by diode conduction voltage drop, and the operational amplifier module eliminates signal attenuation and distortion of a signal sampled at the front end and outputs the signal to the next-stage differential module. And the differential module converts the single-ended signal input by the preceding stage into a differential signal and outputs the differential signal for subsequent processing. Differential signals are superior to single-ended signals in the aspects of interference resistance, electromagnetic compatibility, time sequence positioning, anti-noise capability, low power consumption and flexibility.

Description

Technical Field

[0001] The utility model patent relates to the field of electronic signal processing, specifically a sampling circuit for sampling, rectifying, amplifying and dividing analog signals and converting them into differential signals, so as to facilitate the analog-to-digital converter to perform digital signal conversion. Background Art

[0002] In many data acquisition systems, analog signals need to be converted into digital signals for processing and analysis. Especially in high-precision measurement and signal processing applications, signals often need to be converted into differential signals with stronger anti-interference capabilities and digitized through analog-to-digital converters. Existing solutions may include multiple independent circuits to complete these steps, resulting in complex, bulky and costly systems. Utility Model Content

[0003] In order to solve the above problems, the utility model provides a high-frequency voltage sampling circuit, including a precision rectifier module, an operational amplifier module and a differential module; the input end of the precision rectifier module is connected to an AC voltage, and the output end is connected to the input end of the operational amplifier module; the output end of the operational amplifier module is connected to the input end of the differential module; the differential module transmits a sampling signal through a pair of differential lines, and the signal amplitudes on the pair of differential lines are equal but the phases are opposite.

[0004] Further, the differential module includes a differential amplifier chip, a common-phase input resistor R14, a common-phase feedback resistor R15, an inverting input resistor R16, an inverting feedback resistor R17, an input filter capacitor C2, an output resistor R18, an output resistor R19 and an output filter capacitor C5;

[0005] The input filter capacitor C2 is connected to the output end of the operational amplifier module, and the other end is grounded. One end of the input filter capacitor C2 is also connected to the positive input end of the differential amplifier chip through the in-phase input resistor R14;

[0006] The negative feedback end of the differential amplifier chip is connected to the positive input end of the differential amplifier chip through the in-phase feedback resistor R15; the negative input end of the differential amplifier chip is grounded through the inverting input resistor R16, and the positive feedback end of the differential amplifier chip is connected to the negative input end of the differential amplifier chip through the inverting feedback resistor R17; the negative output end and the positive output end of the differential amplifier chip output sampling signals through the output resistor R18 and the output resistor R19 respectively; the output filter capacitor C5 is connected to one end of the output resistor R18 and the output resistor R19 away from the negative output end and the positive output end of the differential amplifier chip.

[0007] Furthermore, the operational amplifier module includes a first-stage operational amplifier unit, a second-stage operational amplifier unit and a third-stage operational amplifier unit connected in series in sequence, and a voltage divider unit; the input end of the first-stage operational amplifier unit is connected to the output end of the precision rectifier module and the AC voltage, and the output end of the third-stage operational amplifier unit is the output end of the operational amplifier module; one end of the voltage divider unit is connected to the output end of the second-stage operational amplifier unit, one end is connected to the input end of the third-stage operational amplifier unit, and the other end is grounded.

[0008] Furthermore, the first-stage operational amplifier unit includes a first operational amplifier, an input resistor R3, an input resistor R4, an input resistor R5 and a feedback resistor R6; one end of the input resistor R3 is connected to the AC voltage, and the other end is connected to the inverting input of the first operational amplifier; the non-inverting input of the first operational amplifier is grounded; the output of the first operational amplifier is connected to the next-stage unit, and is connected to the inverting input of the first operational amplifier through the feedback resistor R6; the input resistor R4 and the input resistor R5 are connected in parallel, one end of which is connected to the precision rectifier module, and the other end is connected to the inverting input of the first operational amplifier.

[0009] Furthermore, the secondary operational amplifier unit includes a second operational amplifier, an input resistor R7 and a feedback resistor R8; one end of the input resistor R7 is connected to the output end of the first operational amplifier unit, and the other end is connected to the inverting input end of the second operational amplifier; the output end of the second operational amplifier is connected to the next level unit, and is connected to the inverting input end of the second operational amplifier through the feedback resistor R8; the non-inverting input end of the second operational amplifier is grounded.

[0010] Furthermore, the three-stage operational amplifier unit includes a third operational amplifier, a feedback resistor R12 and a current limiting resistor R13; one end of the feedback resistor R12 is connected to the inverting input end of the third operational amplifier, and the other end is connected to one end of the current limiting resistor R13; one end of the current limiting resistor R13 is connected to the output end of the third operational amplifier, and the other end is connected to the differential module; the non-inverting input end of the third operational amplifier is connected to the voltage divider unit.

[0011] Furthermore, the voltage divider unit includes a voltage divider resistor R9, a voltage divider resistor R10 and a voltage divider resistor R11; one end of the voltage divider resistor R9 is connected to the output end of the secondary operational amplifier unit, and the other end is connected to one end of the voltage divider resistor R10 and the input end of the tertiary operational amplifier unit; the other end of the voltage divider resistor R10 is connected to one end of the voltage divider resistor R11; the other end of the voltage divider resistor R11 is grounded.

[0012] Furthermore, the precision rectifier module includes a fourth operational amplifier, a rectifier diode D1, a rectifier diode D2, an input resistor R1, a feedback resistor R2 and a filter capacitor C1; one end of the filter capacitor C1 is connected to the AC voltage and the other end is grounded; one end of the input resistor R1 is connected to the AC voltage, and the other end is connected to the inverting input end of the fourth operational amplifier, the positive electrode of the rectifier diode D2 and one end of the feedback resistor R2; the other end of the feedback resistor R2 is connected to the negative electrode of the rectifier diode D1 and the input end of the operational amplifier module; the negative electrode of the rectifier diode D2 is connected to the positive electrode of the rectifier diode D1; the in-phase input end of the fourth operational amplifier is grounded, and the output end is connected to the positive electrode of the rectifier diode D1 and the negative electrode of the rectifier diode D1.

[0013] The utility model has the following beneficial effects:

[0014] Through the joint work of the precision rectifier module, the operational amplifier module and the voltage divider module, a differential signal that meets the requirements is finally collected. Among them, the operational amplifier module eliminates the signal attenuation and distortion problems of the signal sampled by the front end and outputs it to the next-level differential module. Then, the differential module converts the single-ended signal input from the previous stage into a differential signal for output for subsequent processing.

[0015] Differential signals are superior to single-ended signals in terms of anti-interference, electromagnetic compatibility, timing positioning, anti-noise capability, low power consumption and flexibility.

[0016] Since differential signals are transmitted using a pair of differential lines, the signal amplitudes on the pair of differential lines are equal but the phases are opposite, and any external interference tends to affect the pair of lines at the same time. Therefore, when the difference between the two signals is calculated at the receiving end, these interferences will cancel each other out, thereby reducing the impact of various interferences on the signal.

[0017] In addition, since the currents in a pair of lines of a differential signal flow in opposite directions, the electromagnetic fields generated cancel each other out, so differential signals have better electromagnetic compatibility than single-ended signals.

[0018] Moreover, differential signals can more accurately determine the signal transition points because they rely on the difference between the two signal lines in a pair of lines rather than the absolute level of a single signal line. This helps improve the timing accuracy of signals at high-speed transmission.

[0019] Differential signals have excellent noise immunity: Due to their inherent design, differential signals can maintain signal integrity in environments with higher noise. This is especially important for high-speed data transmission and communication systems, as they need to maintain reliable performance in noisy environments.

[0020] In addition, in some cases, differential signals can achieve lower power consumption because they can operate at lower voltage swings while maintaining good signal quality. Differential signals also provide more design flexibility, such as being able to easily convert differential signals to single-ended signals, or mix or multiplex them with other differential signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of a high-frequency voltage sampling circuit in one embodiment of the utility model. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings of the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. It goes without saying that the embodiments described are only part of the embodiments of the utility model, not all of the embodiments. The description of these embodiments does not constitute a limitation on the protection scope of the utility model.

[0023] like Figure 1 As shown, a high-frequency voltage sampling circuit according to the utility model includes a precision rectifier module, an operational amplifier module and a differential module; the input end of the precision rectifier module is connected to the AC voltage, and the output end is connected to the input end of the operational amplifier module; the output end of the operational amplifier module is connected to the input end of the differential module; the differential module transmits the sampling signal through a pair of differential lines, and the signal amplitudes on the pair of differential lines are equal but the phases are opposite.

[0024] The differential module includes an input filter capacitor C2, a differential amplifier chip ADA4932, a common-phase input resistor R14, a common-phase feedback resistor R15, an inverting input resistor R16, an inverting feedback resistor R17, output resistors R18 and R19, an output filter capacitor C5, a common-phase input terminal of the differential amplifier chip ADA4932 connected to the output terminal of the previous stage, and an inverting input terminal connected to GND. This stage of differential circuit performs a single-ended to differential operation. The single-ended signal of the previous stage is converted into a differential signal and then output, and the output differential signal is given to the ADC for analog-to-digital conversion processing.

[0025] Furthermore, the differential module includes a differential amplifier chip ADA4932, a common-phase input resistor R14, a common-phase feedback resistor R15, an inverting input resistor R16, an inverting feedback resistor R17, an input filter capacitor C2, an output resistor R18, an output resistor R19 and an output filter capacitor C5.

[0026] One end of the input filter capacitor C2 is connected to the output end of the operational amplifier module, and the other end is connected to GND; pin 1 of the differential amplifier chip ADA4932 is connected to one end of the non-inverting input feedback resistor R15, and the other end of the non-inverting feedback resistor R15 is connected to the non-inverting input resistor R14, pin 2 of ADA4932 is connected to the non-inverting input resistor R14 and the non-inverting feedback resistor R15, pin 3 of ADA4932 is respectively connected to one end of the inverting resistor R16 and the inverting feedback resistor R17, pin 4 of ADA4932 is connected to the other end of the inverting feedback resistor R17, and the other end of the inverting input resistor R16 is connected to GND, pins 9 and 10 of ADA4932 are respectively connected to two output resistors R18 and R19, and the output filter capacitor C5 is on output pins 9 and 10.

[0027] The differential module is composed of an input filter capacitor C2, a differential amplifier chip ADA4932, a non-inverting input resistor R14, a non-inverting feedback resistor R15, an inverting input resistor R16, an inverting feedback resistor R17, output resistors R18 and R19, and an output filter capacitor C5. The non-inverting input terminal of ADA4932 is connected to the output terminal of the previous stage circuit, and its inverting input terminal is grounded. The differential module is responsible for performing the conversion from single-ended signals to differential signals.

[0028] Through this conversion process, the single-ended signal of the previous circuit is converted into a differential output so that it can be provided to the analog-to-digital converter (ADC) for digital processing. The application of differential signals can improve the signal's anti-noise ability and enhance the system's immunity to environmental interference, thereby ensuring the integrity and accuracy of the signal before it is transmitted to the ADC.

[0029] Furthermore, the operational amplifier module includes a primary operational amplifier unit, a secondary operational amplifier unit, a tertiary operational amplifier unit, and a voltage divider unit which are sequentially connected in series.

[0030] The input end of the first-stage operational amplifier unit is connected to the output end of the precision rectifier module and the AC voltage, and the output end of the third-stage operational amplifier unit is the output end of the operational amplifier module; one end of the voltage divider unit is connected to the output end of the second-stage operational amplifier unit, one end is connected to the input end of the third-stage operational amplifier unit, and the other end is grounded.

[0031] Furthermore, the first-stage operational amplifier unit includes an AD712 chip, an input resistor R3, an input resistor R4, an input resistor R5 and a feedback resistor R6.

[0032] One end of the input resistor R3 is connected to the AC voltage, and the other end is connected to the inverting input of the AD712 chip; the in-phase input of the AD712 chip is grounded; the output of the AD712 chip is connected to the next-level unit, and is connected to the inverting input of the AD712 chip through the feedback resistor R6; the input resistor R4 and the input resistor R5 are connected in parallel, one end of which is connected to the precision rectifier module, and the other end is connected to the inverting input of the AD712 chip.

[0033] This first-stage op amp unit uses AD712 as the core component, supplemented by feedback resistor R6, input resistor R3, and parallel input resistors R4 and R5. The inverting input of AD712 directly receives the output signal of the previous stage, while the non-inverting input is grounded. When receiving a sinusoidal AC signal, the input resistor R3 is responsible for collecting the signal from the sampling input and superimposing it with the signal collected from the output of the precision rectifier module by R4 and R5. In this configuration, the resistance ratio of the feedback resistor R6 to the input resistor R3 is set to 1:1. At the same time, the combination of R6 and the parallel input resistors R4 and R5 forms a resistance ratio of 2:1, thereby achieving double amplification of the output signal. Therefore, the precision rectified signal amplified twice and the sampling input signal are summed, and the final output end is a full-wave rectified signal. This full-wave rectified signal is then processed by the inverting input of AD712 and output in an inverted form, completing the full-wave rectification process of the entire signal.

[0034] Furthermore, the secondary operational amplifier unit includes a TL084 chip, an input resistor R7 and a feedback resistor R8.

[0035] One end of the input resistor R7 is connected to the output end of the first-stage operational amplifier unit, and the other end is connected to the inverting input end of the TL084 chip; the output end of the TL084 chip is connected to the next-stage unit, and is connected to the inverting input end of the TL084 chip through the feedback resistor R8; the non-inverting input end of the TL084 chip is grounded.

[0036] The secondary operational amplifier unit is composed of a TL084 chip, a feedback resistor R8 and an input resistor R7. The resistance ratio of the input resistor R7 to the feedback resistor R8 is set to 1:1. The inverting input terminal of the TL084 is connected to the output of the previous stage circuit, while the non-inverting input terminal is grounded. Based on this configuration, the main function of this stage of the operational amplifier unit is to invert the signal output by the previous stage and output the processed signal.

[0037] Furthermore, the three-stage operational amplifier unit includes a third operational amplifier, a feedback resistor R12 and a current limiting resistor R13.

[0038] One end of the feedback resistor R12 is connected to the inverting input end of the TL084 chip, and the other end is connected to one end of the current limiting resistor R13; one end of the current limiting resistor R13 is connected to the output end of the TL084 chip, and the other end is connected to the differential module; the non-inverting input end of the TL084 chip is connected to the voltage divider unit.

[0039] The three-stage op amp unit uses the TL084 chip, combined with the feedback resistor R12 and the current limiting resistor R13. In this unit, the feedback resistor R12 connects the output end and the inverting input end of the TL084. At the same time, the non-inverting input end of the TL084 is connected to the voltage divider unit of the previous stage. This configuration makes the op amp unit of this stage act as a voltage follower, ensuring that the output voltage is the same as the input voltage.

[0040] The voltage follower is designed to effectively eliminate the signal attenuation and distortion caused by the input impedance and ensure the signal quality. In this way, the three-stage op amp unit can transmit the signal of the previous stage without loss, ensuring that the integrity of the signal is maintained.

[0041] Furthermore, the voltage dividing unit includes a voltage dividing resistor R9, a voltage dividing resistor R10 and a voltage dividing resistor R11.

[0042] One end of the voltage-dividing resistor R9 is connected to the output end of the secondary operational amplifier unit, and the other end is connected to one end of the voltage-dividing resistor R10 and the input end of the tertiary operational amplifier unit; the other end of the voltage-dividing resistor R10 is connected to one end of the voltage-dividing resistor R11; the other end of the voltage-dividing resistor R11 is grounded.

[0043] Since the signal at this level exceeds the input range of the next level differential module, this level of voltage divider unit is used.

[0044] Furthermore, the precision rectifier module includes an AD712 chip, a rectifier diode D1, a rectifier diode D2, an input resistor R1, a feedback resistor R2 and a filter capacitor C1; one end of the filter capacitor C1 is connected to the AC voltage and the other end is grounded; one end of the input resistor R1 is connected to the AC voltage, and the other end is connected to the inverting input end of the AD712 chip, the positive electrode of the rectifier diode D2 and one end of the feedback resistor R2; the other end of the feedback resistor R2 is connected to the negative electrode of the rectifier diode D1 and the input end of the operational amplifier module; the negative electrode of the rectifier diode D2 is connected to the positive electrode of the rectifier diode D1; the in-phase input end of the AD712 chip is grounded, and the output end is connected to the positive electrode of the rectifier diode D1 and the negative electrode of the rectifier diode D1.

[0045] Under the positive half-cycle of AC voltage input, the voltage of the inverting input terminal (pin 6) of the AD712 chip is higher than the non-inverting input terminal (pin 5), resulting in a signal opposite to the voltage of pin 6 at the output terminal. Since the voltage value of the output signal is lower than zero, and considering that the conduction voltage of diode D1 is about 0.7V, the diode between the anode (pin 2) and cathode (pin 3) of D1 will not conduct at this time, so the output voltage is zero. Conversely, when the AC voltage is in the negative half-cycle, the voltage of the inverting input terminal (pin 6) of AD712 is lower than the non-inverting input terminal (pin 5), and a positive inverted signal will be generated at the output terminal. Since the signal value of pin 6 is negative, the output signal value after inversion is positive. At this time, the D1 diode is turned on, allowing the output signal to pass, so the output voltage is greater than zero.

[0046] When the input signal is an AC sine wave, the output waveform is processed to retain only the negative half-cycle of the original waveform, and this part of the waveform is output inverted. Due to this processing, the positive half-cycle of the output waveform is removed, and the negative half-cycle is flipped to a positive value, forming a waveform profile similar to a steamed bun. Thanks to the negative feedback mechanism in the circuit, the output signal is able to compensate for the voltage drop loss caused by the forward conduction voltage of the diode. This compensation ensures that the signal will not attenuate as the diode is turned on during the rectification process, maintaining the strength and quality of the signal.

[0047] This precision rectifier module converts the AC input signal into a unidirectional output signal, that is, the signal is allowed to pass only during the negative half cycle, and converted into a positive voltage output, thereby achieving a high-precision rectification function.

[0048] Among them, the 5th, 6th, 7th and 8th pins of ADA4932 are connected to 5V power supply, and the 13th, 14th, 15th and 16th pins are connected to -5V power supply. The 4th pin of AD712 is connected to -15V power supply, and the 8th pin is connected to 15V power supply. The 4th pin of TL084 is connected to -15V power supply, and the 8th pin is connected to 15V power supply.

[0049] Through the joint work of the precision rectifier module, the operational amplifier module and the voltage divider module, a differential signal that meets the requirements is finally collected. Among them, the precision rectifier module converts the AC input signal into a unidirectional output signal, and uses negative feedback to correct the signal loss that may be caused by the diode conduction voltage drop. The operational amplifier module eliminates the signal attenuation and distortion problems of the signal sampled by the front end and outputs it to the next-level differential module. Then, the differential module converts the single-ended signal input from the previous stage into a differential signal for output for subsequent processing.

[0050] Differential signals are superior to single-ended signals in terms of anti-interference, electromagnetic compatibility, timing positioning, anti-noise capability, low power consumption and flexibility.

[0051] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A high frequency voltage sampling circuit, characterized in that: Including precision rectifier module, operational amplifier module and differential module; The input end of the precision rectifier module is connected to the AC voltage, and the output end is connected to the input end of the operational amplifier module; The output end of the operational amplifier module is connected to the input end of the differential module; The differential module transmits a sampling signal through a pair of differential lines, and the signals on the pair of differential lines have equal amplitudes but opposite phases.

2. The high-frequency voltage sampling circuit according to claim 1, characterized in that: The differential module includes a differential amplifier chip, a common-phase input resistor R14, a common-phase feedback resistor R15, an inverting input resistor R16, an inverting feedback resistor R17, an input filter capacitor C2, an output resistor R18, an output resistor R19 and an output filter capacitor C5; The input filter capacitor C2 is connected to the output end of the operational amplifier module, and the other end is grounded. One end of the input filter capacitor C2 is also connected to the positive input end of the differential amplifier chip through the in-phase input resistor R14; The negative feedback terminal of the differential amplifier chip is connected to the positive input terminal of the differential amplifier chip through the in-phase feedback resistor R15; The negative input terminal of the differential amplifier chip is grounded through the inverting input resistor R16, and the positive feedback terminal of the differential amplifier chip is connected to the negative input terminal of the differential amplifier chip through the inverting feedback resistor R17; The negative output terminal and the positive output terminal of the differential amplifier chip output sampling signals through the output resistor R18 and the output resistor R19 respectively; the output filter capacitor C5 is connected to one end of the output resistor R18 and the output resistor R19 away from the negative output terminal and the positive output terminal of the differential amplifier chip.

3. The high-frequency voltage sampling circuit according to claim 1, characterized in that: The operational amplifier module includes a primary operational amplifier unit, a secondary operational amplifier unit, a tertiary operational amplifier unit, and a voltage divider unit which are sequentially connected in series; The input end of the first-stage operational amplifier unit is connected to the output end of the precision rectifier module and the AC voltage, and the output end of the third-stage operational amplifier unit is the output end of the operational amplifier module; one end of the voltage divider unit is connected to the output end of the second-stage operational amplifier unit, one end is connected to the input end of the third-stage operational amplifier unit, and the other end is grounded.

4. A high frequency voltage sampling circuit according to claim 3, characterized in that: The first-stage operational amplifier unit includes a first operational amplifier, an input resistor R3, an input resistor R4, an input resistor R5 and a feedback resistor R6; One end of the input resistor R3 is connected to the AC voltage, and the other end is connected to the inverting input terminal of the first operational amplifier; The non-inverting input terminal of the first operational amplifier is grounded; The output terminal of the first operational amplifier is connected to the next stage unit, and is connected to the inverting input terminal of the first operational amplifier through the feedback resistor R6; The input resistor R4 and the input resistor R5 are connected in parallel, one end of which is connected to the precision rectifier module, and the other end of which is connected to the inverting input end of the first operational amplifier.

5. The high-frequency voltage sampling circuit according to claim 3, characterized in that: The secondary operational amplifier unit includes a second operational amplifier, an input resistor R7 and a feedback resistor R8; One end of the input resistor R7 is connected to the output end of the first-stage operational amplifier unit, and the other end is connected to the inverting input end of the second operational amplifier; The output terminal of the second operational amplifier is connected to the next stage unit, and is connected to the inverting input terminal of the second operational amplifier through the feedback resistor R8; A non-inverting input terminal of the second operational amplifier is grounded.

6. The high-frequency voltage sampling circuit according to claim 3, characterized in that: The three-stage operational amplifier unit includes a third operational amplifier, a feedback resistor R12 and a current limiting resistor R13; One end of the feedback resistor R12 is connected to the inverting input end of the third operational amplifier, and the other end is connected to one end of the current limiting resistor R13; One end of the current limiting resistor R13 is connected to the output end of the third operational amplifier, and the other end is connected to the differential module; The non-inverting input terminal of the third operational amplifier is connected to the voltage dividing unit.

7. The high-frequency voltage sampling circuit according to claim 3, characterized in that: The voltage dividing unit includes a voltage dividing resistor R9, a voltage dividing resistor R10 and a voltage dividing resistor R11; One end of the voltage-dividing resistor R9 is connected to the output end of the secondary operational amplifier unit, and the other end is connected to one end of the voltage-dividing resistor R10 and the input end of the tertiary operational amplifier unit; The other end of the voltage-dividing resistor R10 is connected to one end of the voltage-dividing resistor R11; The other end of the voltage dividing resistor R11 is grounded.

8. The high-frequency voltage sampling circuit according to claim 1, characterized in that: The precision rectifier module includes a fourth operational amplifier, a rectifier diode D1, a rectifier diode D2, an input resistor R1, a feedback resistor R2 and a filter capacitor C1; One end of the filter capacitor C1 is connected to the AC voltage and the other end is grounded; One end of the input resistor R1 is connected to an AC voltage, and the other end is connected to the inverting input end of the fourth operational amplifier, the positive electrode of the rectifier diode D2 and one end of the feedback resistor R2; The other end of the feedback resistor R2 is connected to the cathode of the rectifier diode D1 and the input end of the operational amplifier module; The cathode of the rectifier diode D2 is connected to the anode of the rectifier diode D1; The non-inverting input terminal of the fourth operational amplifier is grounded, and the output terminal is connected to the anode of the rectifier diode D1 and the cathode of the rectifier diode D1.

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