Driving module applied to semiconductor laser

Abstract

The utility model relates to the technical field of semiconductor lasers, in particular to a driving module applied to a semiconductor laser. According to the technical scheme, the circuit comprises an execution unit and a driving device, wherein the execution unit comprises a TEC, an LD and an NTC; the driving device comprises a driving circuit, a constant current source driving circuit, a signal acquisition circuit and an MCU, the driving circuit is in bidirectional connection with the TEC, and the constant current source driving circuit is in bidirectional connection with the LD. According to the utility model, current and wavelength are controllable and adjustable in the aspect of laser driving, and the limitation of traditional fixed locking wavelength is broken; in signal acquisition, through a high-precision operational amplifier and a 1mA sampling circuit, subtle temperature change is accurately acquired, and the problems of low precision and low resolution of traditional voltage division sampling are solved; in TEC driving, high-frequency noise is avoided by constant current source driving, and temperature control precision and stability are improved by combining a PID (Proportion Integration Differentiation) algorithm.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of semiconductor laser, especially to a driving module applied to semiconductor laser. BACKGROUND

[0002] At present, tunable diode laser absorption spectroscopy (TDLAS) is a kind of laser absorption spectroscopy technology, which is widely used in monitoring trace gases in the atmosphere. This technology mainly uses different gases to absorb different wavelengths of laser, uses tunable semiconductor laser to scan the measured gas, and realizes the measurement of gas molecules through the absorption amount. The laser driving current and temperature are two main factors affecting the laser wavelength, which directly affect the stability and accuracy of gas measurement. The traditional direct absorption method modulates the laser wavelength with fixed driving current, although the structure is simple and the cost is low, but the sensitivity is low and it is easy to be disturbed by low frequency; The temperature control system of traditional switch type and PWM pulse width modulation will cause temperature fluctuation and high frequency noise due to its off working mode, which will bring noise interference to the measurement and affect the measurement result.

[0003] To effectively avoid the influence of the above driving mode, the application provides a driving module applied to a semiconductor laser. CONTENT OF UTILITY MODEL

[0004] The utility model aims at the problem of low measurement result of traditional switch type and PWM pulse width modulation temperature control system in the background art, and provides a driving module applied to a semiconductor laser.

[0005] The technical scheme of the utility model: a driving module applied to a semiconductor laser, comprising.

[0006] The execution unit and the driving device, wherein:

[0007] The execution unit comprises a TEC, an LD and an NTC;

[0008] The driving device comprises a driving circuit, a constant current source driving circuit, a signal acquisition circuit and an MCU, the driving circuit is bidirectionally connected with the TEC, the constant current source driving circuit is bidirectionally connected with the LD, the signal acquisition circuit is bidirectionally connected with the NTC, the MCU is connected with the driving circuit, constant current source driving circuit and signal acquisition circuit respectively, and the driving circuit is controlled by PID.

[0009] Optionally, the constant current source driving circuit comprises a REF3025 reference voltage chip, a first AD8606 operational amplifier, a second AD8606 operational amplifier, a resistor R28, a resistor R29, a resistor R30, and a capacitor C36, an input end of the REF3025 reference voltage chip is connected with a power supply VCC 3.3V, a ground end of the REF3025 reference voltage chip is connected with AGND, an output end of the REF3025 reference voltage chip is connected with a reverse input end of the first AD8606 operational amplifier, a same direction input end of the first AD8606 operational amplifier is connected with the reverse input end thereof, an output end of the first AD8606 operational amplifier is connected with one end of the resistor R26, the other end of the resistor R26 is connected with one end of the capacitor C52, the other end of the capacitor C52 is connected with one end of the resistor R27, the other end of the resistor R27 is connected with a same direction input end of the second AD8606 operational amplifier, a reverse input end of the second AD8606 operational amplifier is connected with one end of the resistor R30, the other end of the resistor R30 is connected with an output end of the first AD8606 operational amplifier, an output end of the second AD8606 operational amplifier is connected with one end of the resistor R28, the other end of the resistor R28 is connected with one end of the resistor R29, the other end of the resistor R29 is connected with AGND, one end of the capacitor C36 is connected with a power supply A_VCC 5V, the other end of the capacitor C36 is connected with AGND, and is used for obtaining a voltage value of the temperature sensor thermistor.

[0010] Optionally, the signal acquisition circuit comprises a third AD8606 operational amplifier, a fourth AD8606 operational amplifier, a thermistor, a resistor R31, a resistor R32, a resistor R33, a resistor R34, a resistor R35, a resistor R36, a resistor R37, a capacitor C40, a capacitor C50, a capacitor C51, a capacitor C74, and an inductor L8. One end of the thermistor is connected to one end of the resistor R31 and one end of the resistor R33. The other end of the resistor R31 is connected to AGND. The other end of the resistor R33 is connected to one end of the capacitor C40 and one end of the resistor R35. The other end of the capacitor C40 is connected to AGND. The other end of the resistor R35 is connected to A_VCC5V. The other end of the thermistor is connected to one end of the resistor R32 and one end of the resistor R34. The other end of the resistor R32 is connected to AGND. The other end of the resistor R34 is connected to one end of the capacitor C50 and one end of the resistor R37. The other end of the capacitor C50 is connected to AGND. The other end of the resistor R37 is connected to one end of the inductor L8. The other end of the inductor L8 is connected to A_VCC5V. One end of the capacitor C51 is connected to A_VCC5V. The other end of the capacitor C51 is connected to AGND. One end of the resistor R36 is connected to the same input end of the third AD8606 operational amplifier. The other end of the resistor R36 is connected to the connection point of the resistor R33 and the capacitor C40. The opposite input end of the third AD8606 operational amplifier is connected to the connection point of the resistor R34 and the capacitor C50. The output end of the third AD8606 operational amplifier is connected to the same input end of the fourth AD8606 operational amplifier. The opposite input end of the fourth AD8606 operational amplifier is connected to the same input end thereof. The output end of the fourth AD8606 operational amplifier is connected to one end of the capacitor C74. The other end of the capacitor C74 is connected to AGND. The signal acquisition circuit is used for acquiring the voltage signal of the thermistor and outputting a high-precision temperature sampling voltage signal.

[0011] Optionally, the driving circuit comprises an NMOS tube IRF540N, an AD8065 operational amplifier, a resistor R43, a resistor R46, a capacitor C53, a capacitor C54, a capacitor C55, a capacitor C56, a capacitor C66 and an inductor L7, one end of the resistor R46 is connected to the output end of the AD8065 operational amplifier, the other end of the resistor R46 is connected to the gate of the NMOS tube IRF540N, one end of the resistor R43 is connected to the source of the NMOS tube IRF540N, the other end of the resistor R43 is connected to AGND, one end of the capacitor C54 is connected to the drain of the NMOS tube IRF540N, the other end of the capacitor C54 is connected to a power supply VCC24V, one end of the capacitor C53 is connected to the inverting input end of the AD8065 operational amplifier, the other end of the capacitor C53 is connected to AGND, one end of the capacitor C55 is connected to a power supply A_VCC10V, the other end of the capacitor C55 is connected to AGND, one end of the capacitor C56 is connected to the power supply A_VCC10V, the other end of the capacitor C56 is connected to AGND, one end of the capacitor C66 is connected to the output end of the AD8065 operational amplifier, the other end of the capacitor C66 is connected to AGND, one end of the inductor L7 is connected to the power supply A_VCC10V, and the other end of the inductor L7 is connected to AGND, and is used for driving a Peltier element.

[0012] Optionally, the constant current source driving circuit comprises an AD8605 operational amplifier, a resistor R281K, a resistor R31, a capacitor C46, a capacitor C47 and a 2N7002 MOS tube, one end of the resistor R281K is connected to the same input end of the AD8605 operational amplifier, the other end of the resistor R281K is connected to a DAC_OUT end, one end of the resistor R31 and one end of the capacitor C46 are connected to the inverting input end of the AD8605 operational amplifier, the other end of the resistor R31 is connected to AGND, the other end of the capacitor C46 is connected to the output end of the AD8605 operational amplifier, the output end of the AD8605 operational amplifier is connected to the gate of the 2N7002 MOS tube, the source of the 2N7002 MOS tube is connected to AGND, one end of the capacitor C47 is connected to the drain of the 2N7002 MOS tube, and the other end of the capacitor C47 is connected to an SLD+ end, and is used for providing a modulated and current-controllable driving current for a semiconductor laser.

[0013] Compared with the prior art, the application has at least one of the following beneficial technical effects:

[0014] The utility model discloses a laser driving current signal controllable adjustable, laser wavelength adjustable purpose, effectively avoid the limitation of traditional fixed wavelength locking,

[0015] The analog acquisition circuit built by the high-precision signal acquisition circuit with a high-precision operational amplifier adopts a 1mA sampling circuit, can effectively acquire the subtle changes of the temperature sensor, and convert the changes into a voltage signal detectable by the MCU, thereby effectively overcoming the low precision and low resolution of the traditional voltage division sampling.

[0016] The driving circuit also adopts the constant current source driving mode, realizes the change of the driving mode from the switching type, pulse width modulation to the continuous constant current, effectively avoids the influence of the high-frequency noise caused by the switching on-off and pulse width modulation on the system detection, and utilizes the PID algorithm for control, thereby better improving the precision and stability of the temperature control. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a principle block diagram of a driving module applied to a semiconductor laser;

[0018] Figure 2 It is a constant current source driving circuit diagram;

[0019] Figure 3 It is a signal acquisition circuit diagram;

[0020] Figure 4 It is a driving circuit diagram;

[0021] Figure 5 It is an LD driving circuit diagram;

[0022] Figure 6 It is a control loop structure block diagram of a PID controller. DETAILED DESCRIPTION

[0023] The technical scheme of the utility model will be further explained below in combination with the drawings and specific embodiments.

[0024] EMBODIMENT

[0025] As Figure 1 shown, the utility model provides a kind of driving module applied to semiconductor laser, including execution unit and driving device, execution unit and driving device are explained in detail below.

[0026] In the embodiment, the execution unit includes TEC, LD and NTC;

[0027] Driving device includes driving circuit, constant current source driving circuit, signal acquisition circuit and MCU, the driving circuit is bidirectionally connected with the TEC, the constant current source driving circuit is bidirectionally connected with the LD, the signal acquisition circuit is bidirectionally connected with the NTC, the MCU is connected with the driving circuit, constant current source driving circuit, signal acquisition circuit respectively, and the driving circuit is controlled by PID.

[0028] In the embodiment, the constant current source driving circuit comprises a REF3025 reference voltage chip, a first AD8606 operational amplifier, a second AD8606 operational amplifier, a resistor R28, a resistor R29, a resistor R30, and a capacitor C36. An input end of the REF3025 reference voltage chip is connected to a power supply VCC 3.3V, a ground end of the REF3025 reference voltage chip is connected to AGND, an output end of the REF3025 reference voltage chip is connected to an inverting input end of the first AD8606 operational amplifier, a non-inverting input end of the first AD8606 operational amplifier is connected to the inverting input end thereof, an output end of the first AD8606 operational amplifier is connected to one end of the resistor R26, the other end of the resistor R26 is connected to one end of the capacitor C52, the other end of the capacitor C52 is connected to one end of the resistor R27, the other end of the resistor R27 is connected to a non-inverting input end of the second AD8606 operational amplifier, one end of the resistor R30 connected to an output end of the first AD8606 operational amplifier, an output end of the second AD8606 operational amplifier is connected to one end of the resistor R28, the other end of the resistor R28 is connected to one end of the resistor R29, the other end of the resistor R29 is connected to AGND, one end of the capacitor C36 is connected to a power supply A_VCC 5V, and the other end of the capacitor C36 is connected to AGND, so as to obtain a voltage value of the temperature sensor thermistor. Figure 2 The constant current source driving circuit is used for obtaining a voltage value of the temperature sensor thermistor. Figure 1 The REF3025 reference voltage chip in the AD8606 provides a direct current reference voltage 2.5V, and the voltage passes through two-stage analog circuits composed of AD8606. U16.1 in the figure is a first-stage voltage follower, and the reference voltage 2.5V passes through the inverting input end of the amplifier. According to the principle of virtual short and virtual open of the analog amplifier, the voltage at the non-inverting input end of the amplifier is consistent with that at the inverting input end, that is, 2.5V. U16.2 in the figure is a second-stage non-inverting proportional amplifier circuit, and the amplification multiple is (1+R28 / R29) times. Therefore, the reference voltage signal passes through the second-stage non-inverting proportional amplifier circuit, and the voltage output from pin 7 in the figure is 5V. Finally, a voltage difference of 2.5V is formed between the left and right ends of R30, and the constant current source driving circuit with a current of 1mA is formed through R30.

[0029] The signal acquisition circuit comprises a third AD8606 operational amplifier, a fourth AD8606 operational amplifier, a thermistor, resistors R31, R32, R33, R34, R35, R36, R37, capacitors C40, C50, C51, C74, and an inductor L8. One end of the thermistor is connected to one end of the resistor R31 and one end of the resistor R33, the other end of the resistor R31 is connected to AGND, the other end of the resistor R33 is connected to one end of the capacitor C40 and one end of the resistor R35, the other end of the capacitor C40 is connected to AGND, the other end of the resistor R35 is connected to a power supply A_VCC5V, the other end of the thermistor is connected to one end of the resistor R32 and one end of the resistor R34, the other end of the resistor R32 is connected to AGND, the other end of the resistor R34 is connected to one end of the capacitor C50 and one end of the resistor R37, the other end of the capacitor C50 is connected to AGND, the other end of the resistor R37 is connected to one end of the inductor L8, the other end of the inductor L8 is connected to the power supply A_VCC5V, one end of the capacitor C51 is connected to the power supply A_VCC5V, the other end of the capacitor C51 is connected to AGND, one end of the resistor R36 is connected to the same input end of the third AD8606 operational amplifier, the other end of the resistor R36 is connected to the connection point of the resistor R33 and the capacitor C40, the opposite input end of the third AD8606 operational amplifier is connected to the connection point of the resistor R34 and the capacitor C50, the output end of the third AD8606 operational amplifier is connected to the same input end of the fourth AD8606 operational amplifier, the opposite input end of the fourth AD8606 operational amplifier is connected to the same input end thereof, the output end of the fourth AD8606 operational amplifier is connected to one end of the capacitor C74, the other end of the capacitor C74 is connected to AGND, and the signal acquisition circuit is used for acquiring a voltage signal of the thermistor and outputting a high-precision temperature sampling voltage signal. Figure 3 As shown in the signal acquisition circuit, the signal acquisition circuit is a second part of the acquisition circuit and is also a two-stage analog circuit composed of AD8606. The first stage U19.1 is a subtraction circuit, and a differential signal obtained through the thermistor is converted into a voltage signal with a size of Uout=U2-U3 at the output pin 1 according to the characteristics of the subtraction circuit. The voltage signal is the voltage value of the thermistor. Then, the voltage follower U19.2 is used to finally output a high-precision temperature sampling voltage signal.

[0030] In addition, the driving circuit comprises an NMOS tube IRF540N, an AD8065 operational amplifier, a resistor R43, a resistor R46, a capacitor C53, a capacitor C54, a capacitor C55, a capacitor C56, a capacitor C66 and an inductor L7. One end of the resistor R46 is connected to the output end of the AD8065 operational amplifier, the other end of the resistor R46 is connected to the gate of the NMOS tube IRF540N, one end of the resistor R43 is connected to the source of the NMOS tube IRF540N, the other end of the resistor R43 is connected to AGND, one end of the capacitor C54 is connected to the drain of the NMOS tube IRF540N, the other end of the capacitor C54 is connected to a power supply VCC24V, one end of the capacitor C53 is connected to the inverting input end of the AD8065 operational amplifier, the other end of the capacitor C53 is connected to AGND, one end of the capacitor C55 is connected to a power supply A_VCC10V, the other end of the capacitor C55 is connected to AGND, one end of the capacitor C56 is connected to a power supply A_VCC10V, the other end of the capacitor C56 is connected to AGND, one end of the capacitor C66 is connected to the output end of the AD8065 operational amplifier, the other end of the capacitor C66 is connected to AGND, one end of the inductor L7 is connected to a power supply A_VCC10V, and the other end of the inductor L7 is connected to AGND, for driving a Peltier element. Figure 4 The driving circuit is mainly composed of an NMOS tube IRF540N and an AD8065 operational amplifier. The principle is that the MCU controls the high-precision DAC chip to output a high-precision voltage signal, which is output to the gate of the IRF540N through the voltage follower composed of the AD8065. When the output voltage signal is greater than the threshold voltage of the NMOS, the MOS tube is turned on to form a path, and the voltage output by the DAC passes through the sampling resistor R43 to form a path with a current size of Udac / R43. Thus, the design of the driving circuit is completed.

[0031] In this embodiment, the constant current source driving circuit includes an AD8605 operational amplifier, resistors R281K and R31, capacitors C46 and C47, and a 2N7002 MOSFET. The non-inverting input of the AD8605 operational amplifier is connected to one end of resistor R281K, and the other end of resistor R281K is connected to the DAC_OUT terminal. The inverting input of the AD8605 operational amplifier is connected to one end of resistor R31 and one end of capacitor C46. The other end of resistor R31 is connected to AGND, and the other end of capacitor C46 is connected to the output of the AD8605 operational amplifier. The output of the AD8605 operational amplifier is connected to the gate of the 2N7002 MOSFET. The source of the 2N7002 MOSFET is connected to AGND, and the drain of the 2N7002 MOSFET is connected to one end of capacitor C47. The other end of capacitor C47 is connected to the SLD+ terminal, which is used to provide a modulated and controllable driving current for the semiconductor laser. To obtain a modulated and controllable drive current, this practical application uses a constant current source drive circuit composed of analog operational amplifiers, such as... Figure 5 As shown, the DAC sawtooth wave signal output by the MCU passes through the AD8605, forming a current signal of the same waveform across the sampling resistor R31, thus obtaining a moduloable drive signal.

[0032] like Figure 6 The diagram shows the control loop structure. This embodiment designs a PID-based semiconductor laser temperature control system using NTC resistor-PID current single closed-loop control. The error signal between the user-set target temperature and the actual temperature serves as the closed-loop input. When the temperature changes, the actual measured value changes, and the error between the measured and target values ​​changes. The MCU uses the PID algorithm to control the output current of the drive circuit, thereby controlling the Peltier's heating power and achieving high-precision temperature control.

[0033] This utility model is applied to TEC and LD drive devices for lasers, including an LD drive circuit, a drive circuit, and a high-precision signal detection circuit. The software part uses PID algorithm control. The LD drive circuit is composed of a constant current source drive circuit, which realizes the controllability and adjustability of the laser drive current signal and the laser wavelength, effectively avoiding the limitations of traditional fixed wavelength locking. The high-precision signal acquisition circuit is an analog acquisition circuit built with a high-precision operational amplifier, using a 1mA sampling circuit, which can effectively acquire subtle changes in the temperature sensor and convert them into a voltage signal that can be detected by the MCU, effectively overcoming the shortcomings of low accuracy and low resolution of traditional voltage divider sampling. The drive circuit also adopts a constant current source drive method, realizing the transformation of the drive method from switching type and pulse width modulation to continuous constant current, effectively avoiding the influence of high-frequency noise caused by switching and pulse width modulation on the system detection, and using PID algorithm control to better improve the accuracy and stability of temperature control.

[0034] The above specific embodiments are only several optional embodiments of the present application, and based on the technical scheme of the present application and the related enlightenment of the above embodiments, the person skilled in the art can make various alternative improvements and combinations on the above specific embodiments.

Claims

1. A driving module applied to a semiconductor laser, characterized in that, The application relates to a temperature control system for a laser device, which comprises an execution unit and a driving device, wherein the execution unit comprises a TEC, an LD and an NTC; the driving device comprises a driving circuit, a constant-current source driving circuit, a signal acquisition circuit and an MCU, the driving circuit is bidirectionally connected with the TEC, the constant-current source driving circuit is bidirectionally connected with the LD, the signal acquisition circuit is bidirectionally connected with the NTC, the MCU is connected with the driving circuit, the constant-current source driving circuit and the signal acquisition circuit respectively, and the driving circuit is controlled by a PID. The constant-current source driving circuit comprises a REF3025 reference voltage chip, a first AD8606 operational amplifier, a second AD8606 operational amplifier, resistors R28, R29 and R30 and a capacitor C36, the input end of the REF3025 reference voltage chip is connected with a power supply VCC3.3V, the grounding end of the REF3025 reference voltage chip is connected with AGND, the output end of the REF3025 reference voltage chip is connected with the reverse input end of the first AD8606 operational amplifier, the same direction input end of the first AD8606 operational amplifier is connected with the reverse input end, the output end of the first AD8606 operational amplifier is connected with one end of the resistor R26, the other end of the resistor R26 is connected with one end of the capacitor C52, the other end of the capacitor C52 is connected with one end of the resistor R27, the other end of the resistor R27 is connected with the same direction input end of the second AD8606 operational amplifier, the reverse input end of the second AD8606 operational amplifier is connected with one end of the resistor R30, the other end of the resistor R30 is connected with the output end of the first AD8606 operational amplifier, the output end of the second AD8606 operational amplifier is connected with one end of the resistor R28, the other end of the resistor R28 is connected with one end of the resistor R29, the other end of the resistor R29 is connected with AGND, one end of the capacitor C36 is connected with a power supply A_VCC5V, and the other end of the capacitor C36 is connected with AGND. ​ ​ 2. The driving module applied to a semiconductor laser according to claim 1, wherein, ​ 3. The driving module applied to the semiconductor laser according to claim 1, wherein, The signal acquisition circuit comprises a third AD8606 operational amplifier, a fourth AD8606 operational amplifier, a thermistor, a resistor R31, a resistor R32, a resistor R33, a resistor R34, a resistor R35, a resistor R36, a resistor R37, a capacitor C40, a capacitor C50, a capacitor C51, a capacitor C74 and an inductor L8. One end of the thermistor is connected to one end of the resistor R31 and one end of the resistor R33. The other end of the resistor R31 is connected to AGND. The other end of the resistor R33 is connected to one end of the capacitor C40 and one end of the resistor R35. The other end of the capacitor C40 is connected to AGND. The other end of the resistor R35 is connected to a power supply A_VCC5V. The other end of the thermistor is connected to one end of the resistor R32 and one end of the resistor R34. The other end of the resistor R32 is connected to AGND. The other end of the resistor R34 is connected to one end of the capacitor C50 and one end of the resistor R37. The other end of the capacitor C50 is connected to AGND. The other end of the resistor R37 is connected to one end of the inductor L8. The other end of the inductor L8 is connected to the power supply A_VCC5V. One end of the capacitor C51 is connected to the power supply A_VCC5V. The other end of the capacitor C51 is connected to AGND. One end of the resistor R36 is connected to the same input end of the third AD8606 operational amplifier. The other end of the resistor R36 is connected to the connection point of the resistor R33 and the capacitor C40. The opposite input end of the third AD8606 operational amplifier is connected to the connection point of the resistor R34 and the capacitor C50. The output end of the third AD8606 operational amplifier is connected to the same input end of the fourth AD8606 operational amplifier. The opposite input end of the fourth AD8606 operational amplifier is connected to the same input end thereof. The output end of the fourth AD8606 operational amplifier is connected to one end of the capacitor C74. The other end of the capacitor C74 is connected to AGND.

4. The driving module applied to a semiconductor laser according to claim 1, wherein, The driving circuit comprises an NMOS tube IRF540N, an AD8065 operational amplifier, a resistor R43, a resistor R46, a capacitor C53, a capacitor C54, a capacitor C55, a capacitor C56, a capacitor C66 and an inductor L7, one end of the resistor R46 is connected to the output end of the AD8065 operational amplifier, the other end of the resistor R46 is connected to the gate of the NMOS tube IRF540N, one end of the resistor R43 is connected to the source of the NMOS tube IRF540N, the other end of the resistor R43 is connected to AGND, one end of the capacitor C54 is connected to the drain of the NMOS tube IRF540N, the other end of the capacitor C54 is connected to the power supply VCC24V, one end of the capacitor C53 is connected to the inverting input end of the AD8065 operational amplifier, the other end of the capacitor C53 is connected to AGND, one end of the capacitor C55 is connected to the power supply A_VCC10V, the other end of the capacitor C55 is connected to AGND, one end of the capacitor C56 is connected to the power supply A_VCC10V, the other end of the capacitor C56 is connected to AGND, one end of the capacitor C66 is connected to the output end of the AD8065 operational amplifier, the other end of the capacitor C66 is connected to AGND, one end of the inductor L7 is connected to the power supply A_VCC10V, and the other end of the inductor L7 is connected to AGND.

5. The driving module applied to a semiconductor laser according to claim 1, wherein, The constant current source driving circuit comprises an AD8605 operational amplifier, a resistor R281K, a resistor R31, a capacitor C46, a capacitor C47 and a 2N7002 MOS tube, one end of the resistor R281K is connected to the same input end of the AD8605 operational amplifier, the other end of the resistor R281K is connected to the DAC_OUT end, one end of the resistor R31 and one end of the capacitor C46 are connected to the inverting input end of the AD8605 operational amplifier, the other end of the resistor R31 is connected to AGND, the other end of the capacitor C46 is connected to the output end of the AD8605 operational amplifier, the output end of the AD8605 operational amplifier is connected to the gate of the 2N7002 MOS tube, the source of the 2N7002 MOS tube is connected to AGND, one end of the capacitor C47 is connected to the drain of the 2N7002 MOS tube, and the other end of the capacitor C47 is connected to the SLD+ end.

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