Analog-digital signal conversion circuit

Abstract

The utility model provides an analog-to-digital signal conversion circuit which comprises a signal input module and an impedance conversion module connected with the output end of the signal input module, and the output end of the impedance conversion module is divided into two differential signal branches. The first differential signal branch comprises a differential conversion module and a reverse phase differential signal amplification module arranged at the output end of the differential conversion module, the second differential signal branch comprises a positive phase differential signal amplification module, and the analog-digital signal conversion circuit further comprises an AD chip and a parameter setting module. The input end of the AD chip is provided with more than one group of signal input pins, one group of signal input pins are respectively connected with the output ends of the reverse phase differential signal amplification module and the positive phase differential signal amplification module, and the parameter setting module is used for setting parameters of the AD chip. The beneficial effects of the utility model are that common-mode interference can be effectively suppressed, noise can be filtered out, and signal quality can be improved.

Description

Technical Field

[0001] The utility model relates to the technical field of signal processing, and particularly relates to an analog-to-digital signal conversion circuit. Background Art

[0002] An analog-to-digital conversion circuit is a circuit that converts an analog signal into a digital signal and is connected to a controller, so as to output the digital signal to the controller for data acquisition and operation of the controller. Analog-to-digital conversion has a wide range of applications in all walks of life. The accuracy and noise level of the analog-to-digital conversion circuit are often the key factors affecting the quality of the acquired signal. Therefore, how to improve the accuracy of the analog-to-digital conversion circuit and reduce the noise of the analog-to-digital conversion circuit is an important direction in the R & D process. Content of the Utility Model

[0003] To solve the problem of high noise in the prior art, the utility model provides an analog-to-digital signal conversion circuit.

[0004] The analog-to-digital signal conversion circuit of the utility model includes a signal input module and an impedance conversion module connected to the output end of the signal input module. The output end of the impedance conversion module is divided into two differential signal branches. The first differential signal branch includes a differential conversion module and an inverting differential signal amplification module arranged at the output end of the differential conversion module. The second differential signal branch includes a non-inverting differential signal amplification module. The analog-to-digital signal conversion circuit further includes an AD chip and a parameter setting module. The input end of the AD chip is provided with more than one group of signal input pins, and one group of signal input pins is respectively connected to the output ends of the inverting differential signal amplification module and the non-inverting differential signal amplification module. The parameter setting module is used to set the parameters of the AD chip.

[0005] Further, it further includes a constant current source power supply module, and the constant current source power supply module is connected to the input end of the signal input module.

[0006] Further, the constant current source power supply module includes a constant current source power supply chip and a selection switch. Among them, the power input end of the constant current source power supply chip is connected to the power supply, the power output end of the constant current source power supply chip is connected to the pin 2 of the selection switch, the pin 1 is connected to the signal input module, and the pin 3 is grounded through a resistor.

[0007] Further, a direct current blocking module is respectively arranged at the input end of the differential conversion module, the input ends of the inverting differential signal amplification module and the non-inverting differential signal amplification module.

[0008] Further, the direct current blocking module is a polar capacitor or a filter capacitor. The negative electrode of the polar capacitor is connected to the signal input end, and the positive electrode of the polar capacitor outputs the signal after direct current blocking processing.

[0009] Further, the signal input module includes more than one input channel. One of the input channels includes a first interface, a first inductor, a first capacitor, a second capacitor, a first resistor, and a second resistor. Among them, pin 2 of the first interface is grounded, pin 1 is connected to one end of the first capacitor and the first inductor respectively, the other end of the first capacitor is grounded, the other end of the first inductor outputs a signal through the series-connected second capacitor and second resistor, one end of the second resistor is grounded, and the other end is connected between the first resistor and the signal output end.

[0010] Further, the number of branches of the impedance conversion module is the same as the number of input channels of the signal input module. The first impedance conversion module includes an operational amplifier U303. The operational amplifier U303 includes an operational amplifier U303A. The non-inverting input pin 3 of the operational amplifier U303A is connected to the output end of the signal input module, the inverting input pin 2 is connected to the output pin 1 of the operational amplifier U303A. The negative power supply pin 4 of the operational amplifier U303A is connected to the negative pole of the polarized capacitor C316, one end and the negative power supply of the capacitor C315 respectively. The positive pole of the polarized capacitor C316 and the other end of the capacitor C315 are grounded respectively. The positive power supply pin 8 of the operational amplifier U303A is connected to the positive pole of the polarized capacitor C320, one end and the positive power supply of the capacitor C319 respectively. The negative pole of the polarized capacitor C320 and the other end of the capacitor C319 are grounded respectively.

[0011] Further, the differential conversion module includes an operational amplifier U304. The operational amplifier U304 includes an operational amplifier U304A. The inverting input pin 2 of the operational amplifier U304A is connected to the output end of the impedance conversion module through a resistor R319, and is connected to the output pin 1 of the operational amplifier U304A through a resistor R316. The non-inverting input pin 3 of the operational amplifier U304A is connected to a reference voltage signal. The negative power supply of the operational amplifier U304A is grounded. The positive power supply pin 8 of the operational amplifier U304A is connected to the positive pole of the polarized capacitor C324, one end and the positive power supply of the capacitor C323 respectively. The negative pole of the polarized capacitor C324 and the other end of the capacitor C323 are grounded respectively.

[0012] Further, the input channels of the signal input module are more than two. The second impedance conversion module shares the operational amplifier U303 with the first impedance conversion module. The operational amplifier U303 also includes an operational amplifier U303B. The second impedance conversion module uses the operational amplifier U303B. The inverting input pin 6 of the operational amplifier U303B is connected to the output pin 7 of the operational amplifier U303B. The non-inverting input pin 5 of the operational amplifier U303B is connected to the signal output end of the second signal input channel.

[0013] The differential conversion module of the second path shares the operational amplifier U304 with the differential conversion module of the first path. The operational amplifier U304 also includes the operational amplifier U304B. The second path differential conversion module uses the operational amplifier U304B. The inverting input pin 6 of the operational amplifier U304B is connected to the output terminal of the impedance conversion module through the resistor R333 and is connected to the output pin 7 of the operational amplifier U304B through the resistor R331. The non-inverting input pin 5 of the operational amplifier U304B is connected to the reference voltage signal.

[0014] Further, the inverting differential signal amplification module includes a follower amplifier U306A. The non-inverting input pin 3 of the follower amplifier U306A is connected to the output terminal of the differential conversion module. The output pin 1 of the follower amplifier U306A is connected in series with a resistor R320. The inverting input pin 2 of the follower amplifier U306A is respectively connected to one end of a resistor R315 and one end of a capacitor C314. The other end of the resistor R315 and the other end of the capacitor C314 are respectively connected to both ends of the resistor R320.

[0015] The non-inverting differential signal amplification module includes a follower amplifier U306B. The non-inverting input pin 5 of the follower amplifier U306B is connected to the output terminal of the differential conversion module. The output pin 7 of the follower amplifier U306B is connected in series with a resistor R326. The inverting input pin 6 of the follower amplifier U306B is respectively connected to one end of a resistor R323 and one end of a capacitor C327. The other end of the resistor R323 and the other end of the capacitor C327 are respectively connected to both ends of the resistor R326.

[0016] Compared with the prior art, the beneficial effects of the present utility model are:

[0017] By performing level conversion on the input single-ended signal through the impedance conversion module, and then performing inverting processing on the level-converted signal to convert it into a differential signal, through the combination of differential signals, common-mode interference can be effectively suppressed, noise can be filtered out, and signal quality can be improved;

[0018] By setting a DC blocking module at the input end of each module in the two differential signal branches, unnecessary noise can be further filtered out, thereby further improving signal quality;

[0019] By setting a constant current source power supply module in the signal input module, while not introducing additional noise, it can adapt to various signal output devices such as sensors that require power supply or are passive. By setting a selection switch, compatibility of different signals in one channel can be achieved. Brief Description of the Drawings

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

[0021] Figure 1 It is the structural block diagram of the first embodiment of the present utility model;

[0022] Figure 2 It is the structural principle block diagram of the second embodiment of the present utility model;

[0023] Figure 3 It is the schematic diagram of the AD chip and its peripheral circuits;

[0024] Figure 4 It is the schematic diagram of the signal input module circuit;

[0025] Figure 5 It is the schematic diagram of the constant current source power supply module circuit;

[0026] Figure 6 It is the schematic diagram of the impedance conversion module and two differential signal branches circuits. Detailed implementation manners

[0027] Unless otherwise defined, all the technical and scientific terms used in the present utility model have the same meanings as those commonly understood by those skilled in the technical field to which the present utility model belongs; the terms used in the description of the present utility model are only for the purpose of describing specific embodiments and are not intended to limit the present utility model; the terms "including" and "having" and any variations thereof in the description and claims of the present utility model and the above drawings are intended to cover non-exclusive inclusion. The terms "first", "second", etc. in the description and claims of the present utility model or the above drawings are used to distinguish different objects and not to describe a specific order.

[0028] Referring to "embodiment" in the present utility model means that the specific features, structures or characteristics described in connection with the embodiment can be included in at least one embodiment of the present utility model. The appearance of this phrase in various positions in the description does not necessarily refer to the same embodiment, nor is it an exclusive, independent or alternative embodiment that is mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described in the present utility model can be combined with other embodiments.

[0029] In order to enable those skilled in the art of this technology to better understand the solutions of the present utility model, the following will clearly and completely describe the technical solutions in the embodiments of the present utility model in conjunction with the drawings.

[0030] As shown in Figure 1 Figure 1, as an embodiment of the present utility model, the analog-to-digital signal conversion circuit in this example includes a signal input module and an impedance conversion module connected to the output end of the signal input module. The output end of the impedance conversion module is divided into two differential signal branches. The first differential signal branch includes a differential conversion module and an inverting differential signal amplification module arranged at the output end of the differential conversion module. The second differential signal branch includes a non-inverting differential signal amplification module. The analog-to-digital signal conversion circuit further includes an AD chip and a parameter setting module. The input end of the AD chip is provided with more than one set of signal input pins, and one set of signal input pins is respectively connected to the output ends of the inverting differential signal amplification module and the non-inverting differential signal amplification module. The parameter setting module is used to set the parameters of the AD chip.

[0031] By performing level conversion on the input single-ended signal through the impedance conversion module, and then processing the level-converted signal, through inverting processing, it is converted into a differential signal. In this example, by converting the single-ended signal into differential input, the anti-interference ability of the signal is improved, and the signal-to-noise ratio is improved. Through the combination of differential signals, common-mode interference can be effectively suppressed, noise can be filtered out, and the signal quality is further improved. Through the parameter setting module, parameters such as the sampling rate of the AD chip can be adjusted, and the accuracy of the entire analog-to-digital conversion circuit is improved.

[0032] As the second embodiment of the present utility model, on the basis of the first embodiment, this example further includes a constant current source power supply module, and the constant current source power supply module is connected to the input end of the signal input module. By setting the constant current source power supply module in the signal input module, it can provide effective power supply for the free-field mic and other sensors without introducing additional noise. In addition, the present utility model can adapt to various signal output devices such as sensors that require power supply or do not require a power supply. By setting a selection switch, compatibility of different signals in one channel can be achieved.

[0033] Preferably, a DC blocking module is respectively arranged at the input end of the differential conversion module, the input end of the inverting differential signal amplification module, and the input end of the non-inverting differential signal amplification module. By setting DC blocking modules at the input ends of each module in the two differential signal branches, unnecessary noise is further filtered out, thereby further improving the signal quality.

[0034] As shown in Figures 3 - 6 Figure 2, through the circuit design of the present invention, the accuracy of the entire circuit is further improved. The following will be described in detail in combination with a specific circuit.

[0035] As shown in Figure 3As shown, the AD chip in this example preferably uses the CS5381 AD converter that supports differential input, which has a high-pass filter for eliminating DC offset, a linear-phase anti-aliasing filter, and an overload detection function. It can achieve high-precision conversion of signals and transmit the converted digital signals to the controller for signal acquisition and use.

[0036] The AD chip in this example can support the acquisition of two-channel differential signals. Therefore, this example sets up two signal input modules and two impedance conversion modules for signal processing. Of course, this example also supports the signal processing of one or more channels.

[0037] As Figure 4 shown, the signal input module in this example includes two input channels with the same structure. One of the input channels includes interface J301, first inductor L300, first capacitor C311, second capacitor C301, first resistor R301, and second resistor R302. Among them, pin 2 of the first interface is grounded, pin 1 is respectively connected to one end of the first capacitor C311 and the first inductor. The other end of the first capacitor C311 is grounded, and the other end of the first inductor L300 outputs a signal through the series connection of the second capacitor C301 and the second resistor R302. One end of the second resistor R302 is grounded, and the other end is connected between the first resistor R301 and the signal output end.

[0038] The first capacitor C311 in this example is used for signal anti-interference, while the first inductor L300 and the first capacitor C301 are used for filtering. The resistors R301 and R302 are used for current limiting and voltage limiting to achieve over-current and over-voltage protection.

[0039] As Figure 5 shown, the constant current source power supply module in this example is also two-channel, which are respectively connected to the input ends of the two signal input modules. The first constant current source power supply module in this example includes a constant current source power supply chip U300 and a selection switch SW300. Among them, the power input end of the constant current source power supply chip U300 is connected to the 20M power supply, the power output end of the constant current source power supply chip U300 is connected to pin 2 of the selection switch SW300, pin 1 is connected to the signal input module, and pin 3 is grounded through a resistor.

[0040] The constant current source power supply chip U300 in this example is used to provide a constant current voltage for the signal source. Since the signal source includes devices that need to be powered and devices that do not need to be powered, such as various sensors including vibration sensors, microphones, etc., the selection switch SW300 is used to select the signal output of the devices that need to be powered or the devices that do not need to be powered.

[0041] Preferably, this example also connects an indicator light D301 in series on pin 2 of the selection switch SW300 for intuitively obtaining the working state.

[0042] As Figure 6 shown, the number of branches of the impedance conversion module in this example is the same as the number of input channels of the signal input module. The first impedance conversion module includes an operational amplifier U303. The operational amplifier U303 includes an operational amplifier U303A. The non-inverting input pin 3 of the operational amplifier U303A is connected to the output end of the signal input module, the inverting input pin 2 is connected to the output pin 1 of the operational amplifier U303A. The negative power supply pin 4 of the operational amplifier U303A is respectively connected to the negative electrode of the polarized capacitor C316, one end of the capacitor C315 and the negative power supply. The positive electrode of the polarized capacitor C316 and the other end of the capacitor C315 are respectively grounded. The positive power supply pin 8 of the operational amplifier U303A is respectively connected to the positive electrode of the polarized capacitor C320, one end of the capacitor C319 and the positive power supply. The negative electrode of the polarized capacitor C320 and the other end of the capacitor C319 are respectively grounded.

[0043] The differential conversion module includes an operational amplifier U304. The operational amplifier U304 includes an operational amplifier U304A. The inverting input pin 2 of the operational amplifier U304A is connected to the output end of the impedance conversion module through a resistor R319 and is connected to the output pin 1 of the operational amplifier U304A through a resistor R316. The non-inverting input pin 3 of the operational amplifier U304A is connected to a reference voltage signal. The negative power supply of the operational amplifier U304A is grounded. The positive power supply pin 8 of the operational amplifier U304A is respectively connected to the positive electrode of the polarized capacitor C324, one end of the capacitor C323 and the positive power supply. The negative electrode of the polarized capacitor C324 and the other end of the capacitor C323 are respectively grounded.

[0044] Preferably, the number of input channels of the signal input module is an even number and is set in pairs. The second impedance conversion module shares the operational amplifier U303 with the first impedance conversion module. The operational amplifier U303 also includes an operational amplifier U303B. The second impedance conversion module uses the operational amplifier U303B. The inverting input pin 6 of the operational amplifier U303B is connected to the output pin 7 of the operational amplifier U303B. The non-inverting input pin 5 of the operational amplifier U303B is connected to the signal output end of the second signal input channel.

[0045] The second differential conversion module shares the operational amplifier U304 with the first differential conversion module. The operational amplifier U304 also includes an operational amplifier U304B. The second differential conversion module uses the operational amplifier U304B. The inverting input pin 6 of the operational amplifier U304B is connected to the output end of the impedance conversion module through a resistor R333 and is connected to the output pin 7 of the operational amplifier U304B through a resistor R331. The non-inverting input pin 5 of the operational amplifier U304B is connected to a reference voltage signal.

[0046] The inverting differential signal amplification module includes a follower amplifier U306A. The non-inverting input pin 3 of the follower amplifier U306A is connected to the output end of the differential conversion module. The output pin 1 of the follower amplifier U306A is connected in series with a resistor R320. The inverting input pin 2 of the follower amplifier U306A is respectively connected to one end of a resistor R315 and one end of a capacitor C314. The other end of the resistor R315 and the other end of the capacitor C314 are respectively connected to both ends of the resistor R320.

[0047] The non-inverting differential signal amplification module includes a follower amplifier U306B. The non-inverting input pin 5 of the follower amplifier U306B is connected to the output end of the differential conversion module. The output pin 7 of the follower amplifier U306B is connected in series with a resistor R326. The inverting input pin 6 of the follower amplifier U306B is respectively connected to one end of a resistor R323 and one end of a capacitor C327. The other end of the resistor R323 and the other end of the capacitor C327 are respectively connected to both ends of the resistor R326.

[0048] In this example, the DC blocking module is a polarized capacitor or a filtering capacitor. The negative pole of the polarized capacitor is connected to the signal input end, and the positive pole of the polarized capacitor outputs the signal after DC blocking processing.

[0049] The working principle of this example is as follows:

[0050] The input signal is converted into a suitable level through the impedance conversion module and then divided into two paths. One path is the inverting differential signal, and the other path is the non-inverting differential signal. The inverting differential signal is subjected to DC blocking processing through the polarized capacitor C317, and the first-layer filtering processing of the signal is performed. Then, it is sent to the differential conversion module for inverting signal conversion. After conversion, it is subjected to DC blocking processing through the polarized capacitor C318, and the second-layer filtering processing of the signal is performed. Then, the reference voltage conversion is performed through the resistor R317 and the resistor R322, and it is output to the subsequent follower amplifier U306A to be amplified by an appropriate multiple and then output. The resistor R315 and the capacitor C314 are used for phase matching, and the resistors R320 and R326 arranged after the follower amplifier U306A and the follower amplifier U306B can effectively suppress oscillation.

[0051] The differential signal processed by the circuit of the present invention is finally filtered through the capacitor C325. After multi-layer noise filtering and differential processing, it is finally sent to a high-precision AD chip, thereby realizing the high-precision and low-noise AD signal conversion of the present invention. Through the cooperation of the AD chip of the present invention and other circuits, the present invention can realize the processing of high-dynamic range signals greater than 120dB, with low distortion and a sampling rate as high as 192kHz.

[0052] The above-described specific embodiments are the preferred embodiments of the present utility model, and do not limit the specific implementation scope of the present utility model. The scope of the present utility model includes but is not limited to this specific embodiment. All equivalent changes made in accordance with the present utility model are within the protection scope of the present utility model.

Claims

1. A modulus signal conversion circuit, characterized in that: It includes a signal input module and an impedance conversion module connected to the output end of the signal input module. The output end of the impedance conversion module is divided into two differential signal branches. The first differential signal branch includes a differential conversion module and an inverting differential signal amplification module arranged at the output end of the differential conversion module. The second differential signal branch includes a non-inverting differential signal amplification module. The analog-to-digital signal conversion circuit further includes an AD chip and a parameter setting module. The input end of the AD chip is provided with more than one group of signal input pins, and one group of signal input pins are respectively connected to the output ends of the inverting differential signal amplification module and the non-inverting differential signal amplification module. The parameter setting module is used to set the parameters of the AD chip.

2. The modulus signal conversion circuit according to claim 1, characterized in that: It further includes a constant current source power supply module, and the constant current source power supply module is connected to the input end of the signal input module.

3. The modulus signal conversion circuit according to claim 2, wherein: The constant current source power supply module includes a constant current source power supply chip and a selection switch. Among them, the power input end of the constant current source power supply chip is connected to the power supply, the power output end of the constant current source power supply chip is connected to pin 2 of the selection switch, pin 1 is connected to the signal input module, and pin 3 is grounded through a resistor.

4. The analog-to-digital signal conversion circuit according to claim 1, characterized in that: A direct current blocking module is respectively arranged at the input end of the differential conversion module, the input ends of the inverting differential signal amplification module and the non-inverting differential signal amplification module.

5. The analog signal conversion circuit according to claim 4, characterized in that: The direct current blocking module is a polar capacitor or a filter capacitor. The negative pole of the polar capacitor is connected to the signal input end, and the positive pole of the polar capacitor outputs the signal after direct current blocking processing.

6. The analog-to-digital signal conversion circuit according to any one of claims 1-5, characterized in that: The signal input module includes more than one input channel. One of the input channels includes a first interface, a first inductor, a first capacitor, a second capacitor, a first resistor and a second resistor. Among them, pin 2 of the first interface is grounded, pin 1 is respectively connected to one end of the first capacitor and the first inductor, the other end of the first capacitor is grounded, the other end of the first inductor outputs a signal through the series-connected second capacitor and second resistor, one end of the second resistor is grounded, and the other end is connected between the first resistor and the signal output end.

7. The modulus signal conversion circuit according to any one of claims 1-5, characterized in that: The number of branches of the impedance conversion module is the same as the number of input channels of the signal input module. The first impedance conversion module includes an operational amplifier U303. The operational amplifier U303 includes an operational amplifier U303A. The non-inverting input pin 3 of the operational amplifier U303A is connected to the output end of the signal input module, the inverting input pin 2 is connected to the output pin 1 of the operational amplifier U303A. The negative power supply pin 4 of the operational amplifier U303A is respectively connected to the negative pole of the polar capacitor C316, one end and the negative power supply of the capacitor C315. The positive pole of the polar capacitor C316 and the other end of the capacitor C315 are respectively grounded. The positive power supply pin 8 of the operational amplifier U303A is respectively connected to the positive pole of the polar capacitor C320, one end and the positive power supply of the capacitor C319. The negative pole of the polar capacitor C320 and the other end of the capacitor C319 are respectively grounded.

8. The analog-to-digital signal conversion circuit according to claim 7, wherein: The differential conversion module includes an operational amplifier U304, and the operational amplifier U304 includes an operational amplifier U304A. The inverting input pin 2 of the operational amplifier U304A is connected to the output terminal of the impedance conversion module through a resistor R319 and is connected to the output pin 1 of the operational amplifier U304A through a resistor R316. The non-inverting input pin 3 of the operational amplifier U304A is connected to a reference voltage signal. The negative power supply of the operational amplifier U304A is grounded. The positive power supply pin 8 of the operational amplifier U304A is respectively connected to the positive electrode of a polar capacitor C324, one end of a capacitor C323, and a positive power supply. The negative electrode of the polar capacitor C324 and the other end of the capacitor C323 are respectively grounded.

9. The modulus signal conversion circuit according to claim 8, characterized in that: The input channels of the signal input module are two or more. The second impedance conversion module shares the operational amplifier U303 with the first impedance conversion module. The operational amplifier U303 also includes an operational amplifier U303B. The second impedance conversion module uses the operational amplifier U303B. The inverting input pin 6 of the operational amplifier U303B is connected to the output pin 7 of the operational amplifier U303B. The non-inverting input pin 5 of the operational amplifier U303B is connected to the signal output terminal of the second signal input channel. The second differential conversion module shares the operational amplifier U304 with the first differential conversion module. The operational amplifier U304 also includes an operational amplifier U304B. The second differential conversion module uses the operational amplifier U304B. The inverting input pin 6 of the operational amplifier U304B is connected to the output terminal of the impedance conversion module through a resistor R333 and is connected to the output pin 7 of the operational amplifier U304B through a resistor R331. The non-inverting input pin 5 of the operational amplifier U304B is connected to a reference voltage signal.

10. The modulus signal conversion circuit according to any one of claims 1-5, characterized in that: The inverting differential signal amplification module includes a follower amplifier U306A. The non-inverting input pin 3 of the follower amplifier U306A is connected to the output terminal of the differential conversion module. The output pin 1 of the follower amplifier U306A is connected in series with a resistor R320. The inverting input pin 2 of the follower amplifier U306A is respectively connected to one end of a resistor R315 and one end of a capacitor C314. The other end of the resistor R315 and the other end of the capacitor C314 are respectively connected to both ends of the resistor R320. The non-inverting differential signal amplification module includes a follower amplifier U306B. The non-inverting input pin 5 of the follower amplifier U306B is connected to the output terminal of the differential conversion module. The output pin 7 of the follower amplifier U306B is connected in series with a resistor R326. The inverting input pin 6 of the follower amplifier U306B is respectively connected to one end of a resistor R323 and one end of a capacitor C327. The other end of the resistor R323 and the other end of the capacitor C327 are respectively connected to both ends of the resistor R326.

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