A weak light signal detection circuit based on electron chopping

Abstract

This invention discloses a weak light signal detection circuit based on electronic chopping. A microcontroller generates a square wave signal Vr to control a chopping module, obtaining a weak alternating light signal. A photoelectric conversion circuit converts the weak alternating light signal to obtain a voltage signal V1 containing a DC voltage signal and an alternating voltage signal V2. The alternating voltage signal V2 is output to a non-inverting amplifier circuit, which amplifies the alternating voltage signal V2 to obtain an alternating voltage signal Vs. A bandpass filter circuit filters the alternating voltage signal Vs to obtain an AC sinusoidal voltage signal Va. A phase-sensitive detection circuit multiplies a square wave signal with an amplitude of 1 with the AC sinusoidal voltage signal Va to obtain an alternating voltage signal Vd. A low-pass filter circuit filters the alternating voltage signal Vd to obtain a DC voltage signal VOUT that reflects the intensity of the weak light signal. The advantages are that it achieves miniaturization while maintaining high detection sensitivity and a low detection limit.

Description

Technical Field

[0001] This invention relates to a weak light signal detection circuit, and more particularly to a weak light signal detection circuit based on electronic chopping. Background Technology

[0002] In optical research, the optical signal to be measured may be very weak and subject to noise interference, sometimes even with noise intensity much higher than the measured optical signal. Weak optical signal is a relative quantity; relative to noise, the optical signal is submerged and difficult to detect. Detecting the optical signal from noise is the key technology for current weak optical signal detection circuits. The nature and characteristics of noise determine the detection sensitivity and lower limit of weak optical signal detection circuits; therefore, the key lies in suppressing noise and improving the signal-to-noise ratio (SNR). Chopper modulation circuits can modulate weak optical signals into alternating optical signals, avoiding 1 / f noise and obtaining an alternating optical signal synchronized with the modulation frequency. Lock-in amplifiers, constructed using phase-sensitive detection circuits and low-pass filter circuits, can improve the SNR and enhance the resistance of weak optical signal detection circuits to noise interference.

[0003] Reference 1 (Hu Zhende, Guan Yihua, Xie Jianjun, Jin Qinghui. Development of a weak fluorescence detector based on lock-in amplification [J]. Wireless Communication Technology, 2021, 30(02):50-55+62.) proposes a chopper modulation circuit, the circuit diagram of which is shown below. Figure 1 As shown, the chopper modulation circuit includes a photomultiplier tube, an AD4530-based current / voltage conversion circuit, a chopper modulation circuit, and a non-inverting AC amplifier circuit. It uses a TTL square wave generated by a microcontroller to control an analog switch HC4053 to achieve balanced chopper modulation of the two signals output from operational amplifiers A1 and A2. The working principle of the chopper modulation circuit is as follows: the silicon photomultiplier tube D1 detects a weak fluorescence signal and converts it into a current signal, which is output to the current / voltage conversion circuit. The current / voltage conversion circuit, composed of an ADI fA-level input bias current amplifier ADA4530 and resistor R2, converts the current signal into a DC voltage signal, which is then output to the chopper modulation circuit. The chopper modulation circuit converts the DC voltage signal into an AC square wave signal, which is output to the non-inverting AC amplifier circuit, achieving spectrum shifting. The non-inverting AC amplifier circuit is constructed using voltage series negative feedback and capacitive coupling. The AC square wave signal is amplified by the non-inverting AC amplifier circuit, effectively suppressing the influence of low-frequency DC noise. Although the chopper modulation circuit has achieved miniaturization, it still suffers from errors caused by preamplifier drift, dark current, and low-frequency DC noise, resulting in low detection sensitivity and a high detection limit.

[0004] In recent years, an optical chopper has emerged, the chopping mechanism of which is shown in the figure below. Figure 2As shown, an optical chopper is an electronically controlled fan-type blade, mainly composed of three parts: a main chassis, a chopping mechanism, and connecting cables. The main chassis is the speed control electronics system, and the chopping mechanism includes a chopper base and a mechanical chopper blade. The main chassis controls the rotational speed of the mechanical chopper blade via the connecting cables. The working principle of this optical chopper is as follows: under the control of the speed control electronics system, the mechanical chopper blade rotates at a specific speed, chopping the measured light (continuous light) into periodic intermittent light of a certain frequency, with the interruption time equal to the transmission time. This transforms a constant light source into an alternating square wave light source, converting the DC radiation signal into an AC radiation signal, facilitating subsequent electronic processing. In addition to modulating the measured light, the optical chopper also outputs a reference voltage square wave synchronized with the modulation frequency, used as a reference signal for a lock-in amplifier. Therefore, it is particularly suitable for laser, optical, or microwave measurement systems employing lock-in amplifiers. The optical chopper also employs a dedicated control system (i.e., a speed control electronics system), which allows for convenient and continuous adjustment of the chopper frequency and ensures high stability of the chopper frequency. When a continuous beam of light passes through the aperture formed by the mechanical chopper, it is chopped into segments of pulsed light. Although this optical chopper avoids errors caused by preamplifier drift, dark current, and DC low-frequency noise, and has high detection sensitivity and low detection limit, its overall size is large and difficult to operate because the speed control electronics system uses motor mechanical modulation to control the speed of the mechanical chopper. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a weak light signal detection circuit based on electronic chopping that achieves miniaturization while having high detection sensitivity and low detection limit.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a weak light signal detection circuit based on electronic chopping, comprising a chopping module, a photoelectric conversion circuit, a high-pass filter circuit, a non-inverting amplifier circuit, a band-pass filter circuit, a phase-sensitive detection circuit, a low-pass filter circuit, and a microcontroller. The chopping module, under the control of the microcontroller, modulates the weak light signal into a weak alternating light signal. The photoelectric conversion circuit converts the weak alternating light signal modulated by the chopping module into a voltage signal and outputs it to the high-pass filter circuit. The voltage signal output by the photoelectric conversion circuit is denoted as V1, where V1 includes a DC voltage signal and an alternating voltage signal V2. The high-pass filter circuit filters out the DC voltage signal from the voltage signal V1 to obtain the alternating voltage signal V2, which is then output to the non-inverting amplifier circuit. The non-inverting amplifier circuit amplifies the alternating voltage signal V2 output by the high-pass filter circuit to obtain an alternating voltage signal Vs, which is then output to the band-pass filter circuit. The band-pass filter circuit is used to filter the alternating voltage signal output by the non-inverting amplifier circuit. The voltage signal Vs is filtered to obtain an AC sinusoidal voltage signal Va, which is output to the phase-sensitive detection circuit. The phase-sensitive detection circuit multiplies the AC sinusoidal voltage signal Va with a square wave signal of amplitude 1 using a reference signal Vc to obtain an alternating voltage signal Vd, which is output to the low-pass filter circuit. The reference signal Vc is provided by the microcontroller. The low-pass filter circuit filters the alternating voltage signal Vd output by the phase-sensitive detection circuit to obtain a DC voltage signal VOUT that reflects the intensity of the weak light signal, which is output at its output terminal. The microcontroller can read the DC voltage signal VOUT output by the low-pass filter circuit, thus realizing the detection of the weak light signal. The microcontroller generates two square wave signals with the same frequency and amplitude. One square wave signal is denoted as Vr, which is used to control the chopping module to modulate the weak light signal into a weak alternating light signal, wherein the frequency of the weak alternating light signal is equal to that of the square wave signal Vr. The other square wave signal is output to the phase-sensitive detection circuit as the reference signal Vc.

[0007] The high-pass filter circuit, the in-phase amplifier circuit, the band-pass filter circuit, and the low-pass filter circuit each have an input terminal and an output terminal. The phase-sensitive detection circuit has an input terminal, an output terminal, and a control terminal. The microcontroller is connected to the chopping module, the output terminal of the low-pass filter circuit, and the control terminal of the phase-sensitive detection circuit. The output terminal of the photoelectric conversion circuit is connected to the input terminal of the high-pass filter circuit. The output terminal of the high-pass filter circuit is connected to the input terminal of the in-phase amplifier circuit. The output terminal of the in-phase amplifier circuit is connected to the input terminal of the band-pass filter circuit. The output terminal of the band-pass filter circuit is connected to the input terminal of the phase-sensitive detection circuit. The output terminal of the phase-sensitive detection circuit is connected to the input terminal of the low-pass filter circuit.

[0008] The light-chopping module includes a liquid crystal glass (LCD) glass. The microcontroller is connected to the LCD glass, and the square wave signal Vr controls the on / off state of the current in the LCD glass, thereby controlling its light-transmitting and opaque states. This modulates the weak light signal illuminating the LCD glass into a weak alternating light signal. In this structure, the LCD glass is used to implement the light-chopping module. When the LCD glass is de-energized, the liquid crystal molecules inside it are irregularly dispersed, resulting in an opaque appearance. When the LCD glass is energized, the liquid crystal molecules are neatly arranged, allowing light to pass through freely, resulting in a light-transmitting appearance. Thus, by controlling the energization or de-energization of the LCD glass, the weak light signal is modulated to obtain a weak alternating light signal. This effectively avoids interference from 1 / f noise and other factors affecting the subsequent alternating voltage signal V2, which replaces the weak light signal as the test signal. The LCD glass is small in size and easy to operate.

[0009] The photoelectric conversion circuit includes a silicon photomultiplier tube, a first resistor, and a second resistor. One end of the first resistor is connected to a 27V voltage, and the other end is connected to the cathode of the silicon photomultiplier tube. The anode of the silicon photomultiplier tube is connected to one end of the second resistor, and this connection point serves as the output terminal of the photoelectric conversion circuit. The other end of the second resistor is grounded. This photoelectric conversion circuit directly uses the second resistor to convert current signals (photocurrent and dark current signals) into voltage signals (AC voltage signals generated by the photocurrent signal and DC voltage signals generated by the dark current signal). It eliminates the need for an additional current / voltage conversion circuit, thus avoiding the presence of additional DC voltage signals (i.e., offset voltage) caused by introducing an additional current / voltage conversion circuit. This reduces the impact of offset voltage. The subsequent high-pass filter circuit, with its simple structure, can filter out the DC voltage signal from the voltage signal, resulting in a high-precision AC voltage signal. The combination of the photoelectric conversion circuit and the high-pass filter circuit results in a simple and inexpensive overall structure. It overcomes interference from DC quantities such as the voltage generated by dark current and device offset voltage, lowers the detection limit, filters out out-of-band noise to improve the signal-to-noise ratio, and enhances detection sensitivity.

[0010] The high-pass filter circuit includes a first capacitor and a third resistor. One end of the first capacitor is the input terminal of the high-pass filter circuit, and the other end of the first capacitor is connected to one end of the third resistor, with the connection terminal being the output terminal of the high-pass filter circuit. The other end of the third resistor is grounded.

[0011] The non-inverting amplifier circuit includes a first operational amplifier, a fourth resistor, and a fifth resistor. The first operational amplifier has a non-inverting input terminal, an inverting input terminal, and an output terminal. The non-inverting input terminal of the first operational amplifier is the input terminal of the non-inverting amplifier circuit. The inverting input terminal of the first operational amplifier, one end of the fourth resistor, and one end of the fifth resistor are connected together. The other end of the fifth resistor is grounded. The other end of the fourth resistor is connected to the output terminal of the first operational amplifier, and its connection terminal is the output terminal of the non-inverting amplifier circuit.

[0012] The bandpass filter circuit includes a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, a second operational amplifier, a third operational amplifier, a fourth operational amplifier, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, and a fourteenth resistor. The second, third, and fourth operational amplifiers each have a non-inverting input terminal, an inverting input terminal, and an output terminal. One end of the second capacitor is the input terminal of the bandpass filter circuit. The other end of the second capacitor is connected to one end of the sixth resistor. The other end of the sixth resistor, one end of the seventh resistor, one end of the third capacitor, and one end of the fourth capacitor are connected together. The other end of the seventh resistor is grounded. The other end of the third capacitor, one end of the eighth resistor, and the inverting input terminal of the second operational amplifier are connected together. The non-inverting input terminal of the second operational amplifier is grounded. The other end of the eighth resistor, the other end of the fourth capacitor, and the output terminal of the second operational amplifier are connected together. The output terminal is connected to one end of the ninth resistor. The other end of the ninth resistor, one end of the tenth resistor, one end of the fifth capacitor, and one end of the sixth capacitor are connected together. The other end of the tenth resistor is grounded. The other end of the fifth capacitor and one end of the eleventh resistor are connected to the inverting input terminal of the third operational amplifier. The non-inverting input terminal of the third operational amplifier is grounded. The other end of the eleventh resistor, the other end of the sixth capacitor, the output terminal of the third operational amplifier, and one end of the twelfth resistor are connected together. The other end of the twelfth resistor, one end of the thirteenth resistor, one end of the seventh capacitor, and one end of the eighth capacitor are connected together. The other end of the thirteenth resistor is grounded. The other end of the seventh capacitor and one end of the fourteenth resistor are connected to the inverting input terminal of the fourth operational amplifier. The non-inverting input terminal of the fourth operational amplifier is grounded. The other end of the fourteenth resistor and the other end of the eighth capacitor are connected to the output terminal of the fourth operational amplifier, and their connection terminals are the output terminals of the bandpass filter circuit. In this bandpass filter circuit, the second operational amplifier, the sixth resistor, the seventh resistor, the eighth resistor, the third capacitor, and the fourth capacitor constitute the first second-order filter; the third operational amplifier, the ninth resistor, the tenth resistor, the eleventh resistor, the fifth capacitor, and the sixth capacitor constitute the second second-order filter; and the fourth operational amplifier, the twelfth resistor, the thirteenth resistor, the fourteenth resistor, the seventh capacitor, and the eighth capacitor constitute the third second-order filter. Thus, a filter of up to the sixth order is achieved by cascading three simple second-order filters. When the alternating voltage signal Vs is input, the second capacitor first further filters out the DC voltage in the alternating voltage signal Vs to improve the detection accuracy, and then the signal is filtered by the sixth-order filter, resulting in a better bandpass filtering effect.

[0013] The phase-sensitive detection circuit includes an inverter circuit and an analog switch. The inverter circuit includes a fifth operational amplifier, a fifteenth resistor, and a sixteenth resistor. The fifth operational amplifier has a non-inverting input, an inverting input, and an output. The analog switch has a first input, a second input, a control terminal, and an output. The first input of the analog switch is connected to one end of the fifteenth resistor, and this connection terminal serves as the input terminal of the phase-sensitive detection circuit. The other end of the fifteenth resistor and one end of the sixteenth resistor are connected to the inverting input of the fifth operational amplifier. The non-inverting input of the fifth operational amplifier is grounded. The other end of the sixteenth resistor, the output of the fifth operational amplifier, and the second input port of the analog switch are connected. The output of the analog switch serves as the output terminal of the phase-sensitive detection circuit. This phase-sensitive detection circuit utilizes the first analog switch to multiply a square wave signal with an amplitude of ±1 by an AC sinusoidal voltage signal Va. The output signal amplitude is unaffected by the reference signal amplitude, eliminating nonlinearity issues. Its circuit is simple, operates quickly, and is beneficial for reducing costs and increasing circuit operating speed.

[0014] The low-pass filter circuit includes a seventeenth resistor and a ninth capacitor. One end of the seventeenth resistor is the input terminal of the low-pass filter circuit, and the other end of the seventeenth resistor is connected to one end of the ninth capacitor, with the connection terminal being the output terminal of the low-pass filter circuit. The other end of the ninth capacitor is grounded.

[0015] Compared with the prior art, the advantage of this invention lies in the fact that a square wave signal Vr generated by a microcontroller controls the on / off state of the current in the chopper module, thereby achieving chopping modulation of the weak light signal to obtain a weak alternating light signal with the same intensity. The photoelectric conversion circuit further converts the weak alternating light signal to obtain a voltage signal V1 output containing a DC voltage signal and an alternating voltage signal V2. The alternating voltage signal V2 is then output as the signal to be measured to a non-inverting amplifier circuit, which amplifies the alternating voltage signal V2 to obtain an alternating voltage signal Vs, which is then output to a bandpass filter. The phase-sensitive detection circuit uses a bandpass filter to filter the alternating voltage signal Vs, obtaining an AC sinusoidal voltage signal Va, which is then output to the phase-sensitive detection circuit. The phase-sensitive detection circuit multiplies the AC sinusoidal voltage signal Va with a square wave signal of amplitude 1 using a reference signal Vc, resulting in an alternating voltage signal Vd, which is output to the low-pass filter circuit. The reference signal Vc is provided by the microcontroller. The low-pass filter circuit filters the alternating voltage signal Vd output from the phase-sensitive detection circuit, obtaining a DC voltage signal VOUT reflecting the intensity of the weak light signal, which is output at its terminal. This invention enables the detection of weak light signals by reading the DC voltage signal VOUT output from the low-pass filter circuit. It uses an alternating voltage signal V2 instead of the weak light signal as the test signal, avoiding interference from dark current, device offset voltage, and 1 / f noise caused by the direct conversion of the weak light signal (DC signal) into the test signal (DC voltage) by the photoelectric conversion circuit. This avoids the problem of the weak test signal being easily submerged and difficult to measure. The high-pass filter circuit filters out the DC voltage signal in the voltage signal V1, leaving the AC component (i.e., the alternating voltage signal V2), overcoming the interference from DC quantities such as the voltage generated by dark current and device offset voltage, thereby lowering the detection limit, filtering out out-of-band noise to improve the signal-to-noise ratio, and increasing detection sensitivity. This ensures that the detected DC voltage signal VOUT reflects the intensity of the weak light signal. Therefore, this invention is implemented using only a chopper module, photoelectric conversion circuit, high-pass filter circuit, in-phase amplifier circuit, band-pass filter circuit, phase-sensitive detection circuit, low-pass filter circuit, and microcontroller, achieving miniaturization while maintaining high detection sensitivity and a low detection limit. Attached Figure Description

[0016] Figure 1 This is a chopper circuit diagram for weak fluorescence detection disclosed in document 1 of the prior art;

[0017] Figure 2 A chopper mechanical diagram of an optical chopper disclosed in the prior art;

[0018] Figure 3 This is a block diagram of the weak light signal detection circuit based on electronic chopping according to the present invention.

[0019] Figure 4The circuit diagram shows the photoelectric conversion circuit, high-pass filter circuit, and non-inverting amplifier circuit of the weak light signal detection circuit based on electronic chopping of the present invention.

[0020] Figure 5 This is a circuit diagram of the bandpass filter circuit of the weak light signal detection circuit based on electronic chopping of the present invention.

[0021] Figure 6 This is a circuit diagram of the phase-sensitive detection circuit and low-pass filter circuit of the weak light signal detection circuit based on electronic chopping of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0023] Example 1: As Figure 3 As shown, a weak light signal detection circuit based on electronic chopping includes a chopping module, a photoelectric conversion circuit, a high-pass filter circuit, a non-inverting amplifier circuit, a band-pass filter circuit, a phase-sensitive detection circuit, a low-pass filter circuit, and a microcontroller. The chopping module, under the control of the microcontroller, modulates the weak light signal into a weak alternating light signal. The photoelectric conversion circuit converts the weak alternating light signal modulated by the chopping module into a voltage signal, which is output to the high-pass filter circuit. The voltage signal output by the photoelectric conversion circuit is denoted as V1, which contains a DC voltage signal and an alternating voltage signal V2. The high-pass filter circuit filters out the DC voltage signal from the voltage signal V1 to obtain the alternating voltage signal V2, which is output to the non-inverting amplifier circuit. The non-inverting amplifier circuit amplifies the alternating voltage signal V2 output from the high-pass filter circuit to obtain an alternating voltage signal Vs, which is output to the band-pass filter circuit. The band-pass filter circuit filters the alternating voltage signal Vs output from the non-inverting amplifier circuit. The AC sinusoidal voltage signal Va is output to the phase-sensitive detection circuit. The phase-sensitive detection circuit multiplies the AC sinusoidal voltage signal Va with a square wave signal of amplitude 1 using the reference signal Vc to obtain an alternating voltage signal Vd, which is then output to the low-pass filter circuit. The reference signal Vc is provided by the microcontroller. The low-pass filter circuit filters the alternating voltage signal Vd output by the phase-sensitive detection circuit to obtain a DC voltage signal VOUT that reflects the intensity of the weak light signal. The microcontroller can read the DC voltage signal VOUT output by the low-pass filter circuit, thus realizing the detection of the weak light signal. The microcontroller generates two square wave signals with the same frequency and amplitude. One square wave signal is denoted as Vr. The square wave signal Vr is used to control the chopping module to modulate the weak light signal into a weak alternating light signal, where the frequency of the weak alternating light signal is equal to that of the square wave signal Vr. The other square wave signal is output to the phase-sensitive detection circuit as the reference signal Vc.

[0024] In this embodiment, the high-pass filter circuit, the in-phase amplifier circuit, the band-pass filter circuit, and the low-pass filter circuit each have an input terminal and an output terminal. The phase-sensitive detection circuit has an input terminal, an output terminal, and a control terminal. The microcontroller is connected to the chopper module, the output terminal of the low-pass filter circuit, and the control terminal of the phase-sensitive detection circuit, respectively. The output terminal of the photoelectric conversion circuit is connected to the input terminal of the high-pass filter circuit. The output terminal of the high-pass filter circuit is connected to the input terminal of the in-phase amplifier circuit. The output terminal of the in-phase amplifier circuit is connected to the input terminal of the band-pass filter circuit. The output terminal of the band-pass filter circuit is connected to the input terminal of the phase-sensitive detection circuit. The output terminal of the phase-sensitive detection circuit is connected to the input terminal of the low-pass filter circuit.

[0025] Example 2: This example is basically the same as the previous example, except that:

[0026] In this embodiment, as Figure 4 As shown, the light-chopping module includes a liquid crystal glass (LCD) and a microcontroller connected to it. A square wave signal Vr controls the on / off state of the current in the LCD, thereby controlling its light-transmitting and light-blocking states, modulating the weak light signal illuminating the LCD into a weak alternating light signal. The photoelectric conversion circuit includes a silicon photomultiplier tube (SiPM), a first resistor R1, and a second resistor R2. One end of the first resistor R1 is connected to a 27V voltage, and the other end is connected to the cathode of the SiPM. The anode of the SiPM is connected to one end of the second resistor R2, and this connection point is the output terminal of the photoelectric conversion circuit. The other end of the second resistor R2 is grounded. The high-pass filter circuit includes a first capacitor C1 and a third resistor R3. One end of the first capacitor C1 is the input terminal of the high-pass filter circuit, and the other end is connected to one end of the third resistor R3, which is the output terminal of the high-pass filter circuit. The other end of the third resistor R3 is grounded. The non-inverting amplifier circuit includes a first operational amplifier A1, a fourth resistor R4, and a fifth resistor R5. The first operational amplifier A1 has a non-inverting input terminal, an inverting input terminal, and an output terminal. The non-inverting input terminal of the first operational amplifier A1 is the input terminal of the non-inverting amplifier circuit. The inverting input terminal of the first operational amplifier A1, one end of the fourth resistor R4, and one end of the fifth resistor R5 are connected. The other end of the fifth resistor R5 is grounded. The other end of the fourth resistor R4 is connected to the output terminal of the first operational amplifier A1, and its connection terminal is the output terminal of the non-inverting amplifier circuit.

[0027] like Figure 5As shown, the bandpass filter circuit includes capacitors C2, C3, C4, C5, C6, C7, C8, operational amplifiers A2, A3, and A4, resistors R6, R7, R8, R9, R10, R11, R12, R13, and R14, and operational amplifiers A2, A3, and A4. Each of A4 has a non-inverting input, an inverting input, and an output. One end of the second capacitor C2 is the input of the bandpass filter circuit. The other end of the second capacitor C2 is connected to one end of the sixth resistor R6. The other end of the sixth resistor R6, one end of the seventh resistor R7, one end of the third capacitor C3, and one end of the fourth capacitor C4 are connected together. The other end of the seventh resistor R7 is grounded. The other end of the third capacitor C3, one end of the eighth resistor R8, and the inverting input of the second operational amplifier A2 are connected together. The non-inverting input of the second operational amplifier A2 is grounded. The other end of the eighth resistor R8, the inverting input of the second operational amplifier A2, and the non-inverting input of the second operational amplifier A2 are all connected together. The other end of capacitor C4, the output of the second operational amplifier A2, and one end of the ninth resistor R9 are connected. The other end of the ninth resistor R9, one end of the tenth resistor R10, one end of the fifth capacitor C5, and one end of the sixth capacitor C6 are connected. The other end of the tenth resistor R10 is grounded. The other end of the fifth capacitor C5, one end of the eleventh resistor R11, and the inverting input of the third operational amplifier A3 are connected. The non-inverting input of the third operational amplifier A3 is grounded. The other end of the eleventh resistor R11, the other end of the sixth capacitor C6, and the output of the third operational amplifier A3 are connected to... One end of the twelfth resistor R12 is connected, the other end of the twelfth resistor R12, one end of the thirteenth resistor R13, one end of the seventh capacitor C7, and one end of the eighth capacitor C8 are connected, the other end of the thirteenth resistor R13 is grounded, the other end of the seventh capacitor C7, one end of the fourteenth resistor R14 is connected to the inverting input of the fourth operational amplifier A4, the non-inverting input of the fourth operational amplifier A4 is grounded, and the other end of the fourteenth resistor R14, the other end of the eighth capacitor C8, and the output of the fourth operational amplifier A4 are connected, and the connection point is the output of the bandpass filter circuit.

[0028] like Figure 6As shown, the phase-sensitive detection circuit includes an inverter circuit and an analog switch K1. The inverter circuit includes a fifth operational amplifier A5, a fifteenth resistor R15, and a sixteenth resistor R16. The fifth operational amplifier A5 has a non-inverting input terminal, an inverting input terminal, and an output terminal. The analog switch K1 has a first input terminal, a second input terminal, a control terminal, and an output terminal. The first input terminal of the analog switch K1 is connected to one end of the fifteenth resistor R15, and this connection terminal is the input terminal of the phase-sensitive detection circuit. The other end of the fifteenth resistor R15 and one end of the sixteenth resistor R16 are connected to the inverting input terminal of the fifth operational amplifier A5. The non-inverting input terminal of the fifth operational amplifier A5 is grounded. The other end of the sixteenth resistor R16, the output terminal of the fifth operational amplifier A5, and the second input port of the analog switch K1 are connected. The output terminal of the analog switch K1 is the output terminal of the phase-sensitive detection circuit. The low-pass filter circuit includes a seventeenth resistor R17 and a ninth capacitor C9. One end of the seventeenth resistor R17 is the input terminal of the low-pass filter circuit, and the other end of the seventeenth resistor R17 is connected to one end of the ninth capacitor C9, and the connection terminal is the output terminal of the low-pass filter circuit. The other end of the ninth capacitor C9 is grounded.

[0029] The working principle of the weak light signal detection circuit based on electronic chopping in this embodiment is as follows: When weak light signal detection is performed, the chopping module is connected to an external power supply. The microcontroller generates a square wave signal Vr and a reference signal Vc. The square wave signal Vr controls the on / off state of the current in the chopping module. Under the control of the square wave signal Vr, the chopping module modulates the weak light signal input into it into a weak alternating light signal. The frequency of the weak alternating light signal is equal to that of the square wave signal Vr, and the intensity of the weak alternating light signal is proportional to the intensity of the weak light signal. When the frequency of the weak alternating light signal remains constant, the intensity of the weak alternating light signal is proportional to the number of photons in the weak alternating light signal per unit time. Therefore, the number of photons in the weak alternating light signal is proportional to the intensity of the weak light signal. When a silicon photomultiplier tube (SiPM) captures photons generated by a weak alternating light signal, it produces a corresponding photocurrent signal. The number of photons in the weak alternating light signal is directly proportional to the magnitude of the photocurrent signal generated by the SiPM; that is, the intensity of the weak light signal is also directly proportional to the photocurrent signal generated by the SiPM. The magnitude of the photocurrent signal generated by the SiPM indirectly reflects the intensity of the weak light signal. When the photoelectric conversion circuit does not receive the weak alternating light signal modulated by the chopper module, the SiPM only generates a DC current signal output, which is called the dark current signal. When the photoelectric conversion circuit receives the weak alternating light signal modulated by the chopper module, the SiPM simultaneously converts the weak alternating light signal into a corresponding photocurrent signal output. At this time, the SiPM outputs a current signal including both the photocurrent signal and the dark current signal. This current signal flows through the second resistor R2, resulting in a voltage signal V1, which is output at the output terminal of the photoelectric conversion circuit. Voltage signal V1 comprises a DC voltage signal and an alternating voltage signal V2. The DC voltage signal corresponds to the dark current signal and 1 / f noise, while the alternating voltage signal V2 corresponds to the photocurrent signal I1 and the two are proportional. Voltage signal V1 is output to a high-pass filter circuit. The high-pass filter circuit filters out the DC voltage signal from voltage signal V1 through the first capacitor C1 and the third resistor R3, obtaining the alternating voltage signal V2, which is then output to a non-inverting amplifier circuit. The main function of the non-inverting amplifier circuit is to amplify the alternating voltage signal V2 to obtain an alternating voltage signal Vs sufficient to drive the phase-sensitive detector. The alternating voltage signal output by the non-inverting amplifier circuit... In this circuit, R4 represents the resistance of the fourth resistor, R5 represents the resistance of the fifth resistor, and the bandpass filter circuit is a frequency selection circuit. The bandpass filter circuit filters out out-of-band noise from the alternating voltage signal Vs output by the in-phase amplifier circuit, leaving only the signal within the desired frequency range, resulting in an AC sinusoidal voltage signal denoted as Va. The AC sinusoidal voltage signal Va output by the bandpass filter circuit is proportional to V2, meaning that the AC sinusoidal voltage signal Va is proportional to the intensity of the weak light signal. In the phase-sensitive detection circuit, the reference signal Vc is input to the control terminal of the analog switch K1, and the AC sinusoidal voltage signal Va is input to the inverting circuit. The inverter circuit inverts the AC sinusoidal voltage signal Va to obtain an inverted voltage signal Vb. The inverted voltage signal Vb has the same amplitude as the AC sinusoidal voltage signal Va but is 180 degrees out of phase. The AC sinusoidal voltage signal Va is input to the first input terminal of analog switch K1, and the inverted voltage signal Vb is input to the second input terminal of analog switch K1. The output terminal of analog switch K1 outputs an alternating voltage signal Vd. The reference signal Vc is a square wave signal, which can be represented by high or low levels. If the reference signal Vc is high, then the first input terminal of analog switch K1... When the first input terminal of analog switch K1 is connected to its output terminal, and the second input terminal is connected to its output terminal, the alternating voltage signal Vd output by analog switch K1 is an AC sinusoidal voltage signal Va, which is equivalent to multiplying the AC sinusoidal voltage signal Va by the logic value 1 corresponding to the high level. When the reference signal Vc is low, the first input terminal and its output terminal of analog switch K1 are cut off, and the second input terminal and its output terminal are connected. The alternating voltage signal Vd output by analog switch K1 is an inverted voltage signal Vb, which is equivalent to multiplying the AC sinusoidal voltage signal Va by the logic value 1 corresponding to the low level. Multiplying by -1, the phase-sensitive detection circuit multiplies a square wave signal with an amplitude of ±1 with an AC sinusoidal voltage signal Va to obtain an alternating voltage signal Vd. A low-pass filter circuit filters the alternating voltage signal Vd to obtain a DC voltage signal VOUT, which is output. The microcontroller reads the DC voltage signal VOUT output from the low-pass filter circuit. Since the DC voltage signal VOUT is proportional to the AC sinusoidal voltage signal Va, it is proportional to the intensity of the weak light signal, thus enabling the detection of the weak light signal. The DC voltage signal VOUT has the largest amplitude when the reference signal Vc and the AC sinusoidal voltage signal Va are in phase. By controlling the phase of the reference signal Vc to be in phase with the AC sinusoidal voltage signal Va, the DC voltage signal VOUT with the maximum amplitude can be obtained.

Claims

1. A weak optical signal detection circuit based on electron chopping, characterized in that... The system includes a chopping module, a photoelectric conversion circuit, a high-pass filter circuit, a non-inverting amplifier circuit, a band-pass filter circuit, a phase-sensitive detection circuit, a low-pass filter circuit, and a microcontroller. The chopping module, under the control of the microcontroller, modulates a weak light signal into a weak alternating light signal. The photoelectric conversion circuit converts the modulated weak alternating light signal into a voltage signal, which is output to the high-pass filter circuit. The voltage signal output by the photoelectric conversion circuit is denoted as V1, which contains a DC voltage signal and an alternating voltage signal V2. The high-pass filter circuit filters out the DC voltage signal from V1 to obtain the alternating voltage signal V2, which is then output to the non-inverting amplifier circuit. The non-inverting amplifier circuit amplifies the alternating voltage signal V2 output from the high-pass filter circuit to obtain an alternating voltage signal Vs, which is then output to the band-pass filter circuit. The band-pass filter circuit filters the alternating voltage signal Vs output from the non-inverting amplifier circuit to obtain an AC sinusoidal voltage signal V. The signal a is output to the phase-sensitive detection circuit. The phase-sensitive detection circuit multiplies a square wave signal with an amplitude of 1 by an AC sinusoidal voltage signal Va to obtain an alternating voltage signal Vd, which is then output to the low-pass filter circuit. The reference signal Vc is provided by the microcontroller. The low-pass filter circuit filters the alternating voltage signal Vd output by the phase-sensitive detection circuit to obtain a DC voltage signal VOUT that reflects the intensity of the weak light signal. The microcontroller can read the DC voltage signal VOUT output by the low-pass filter circuit, thus realizing the detection of the weak light signal. The microcontroller generates two square wave signals with the same frequency and amplitude. One square wave signal is denoted as Vr. The square wave signal Vr is used to control the chopping module to modulate the weak light signal into a weak alternating light signal, wherein the frequency of the weak alternating light signal is equal to that of the square wave signal Vr. The other square wave signal is output to the phase-sensitive detection circuit as the reference signal Vc.

2. The weak light signal detection circuit based on electron chopping according to claim 1, characterized in that... The high-pass filter circuit, the in-phase amplifier circuit, the band-pass filter circuit, and the low-pass filter circuit each have an input terminal and an output terminal. The phase-sensitive detection circuit has an input terminal, an output terminal, and a control terminal. The microcontroller is connected to the chopping module, the output terminal of the low-pass filter circuit, and the control terminal of the phase-sensitive detection circuit. The output terminal of the photoelectric conversion circuit is connected to the input terminal of the high-pass filter circuit. The output terminal of the high-pass filter circuit is connected to the input terminal of the in-phase amplifier circuit. The output terminal of the in-phase amplifier circuit is connected to the input terminal of the band-pass filter circuit. The output terminal of the band-pass filter circuit is connected to the input terminal of the phase-sensitive detection circuit. The output terminal of the phase-sensitive detection circuit is connected to the input terminal of the low-pass filter circuit.

3. A weak light signal detection circuit based on electronic chopping according to claim 1 or 2, characterized in that... The light-chopping module includes a liquid crystal glass, the microcontroller is connected to the liquid crystal glass, and the square wave signal Vr is used to control the on and off of the current in the liquid crystal glass, thereby controlling the light-transmitting and light-blocking states of the liquid crystal glass, so that the weak light signal illuminating the liquid crystal glass is modulated into a weak alternating light signal.

4. The weak light signal detection circuit based on electron chopping according to claim 2, characterized in that... The photoelectric conversion circuit includes a silicon photomultiplier tube, a first resistor, and a second resistor. One end of the first resistor is connected to a 27V voltage, and the other end of the first resistor is connected to the cathode of the silicon photomultiplier tube. The anode of the silicon photomultiplier tube is connected to one end of the second resistor, and the connection end is the output terminal of the photoelectric conversion circuit. The other end of the second resistor is grounded.

5. A weak light signal detection circuit based on electron chopping according to claim 2, characterized in that... The high-pass filter circuit includes a first capacitor and a third resistor. One end of the first capacitor is the input terminal of the high-pass filter circuit, and the other end of the first capacitor is connected to one end of the third resistor, with the connection terminal being the output terminal of the high-pass filter circuit. The other end of the third resistor is grounded.

6. A weak light signal detection circuit based on electron chopping according to claim 2, characterized in that... The non-inverting amplifier circuit includes a first operational amplifier, a fourth resistor, and a fifth resistor. The first operational amplifier has a non-inverting input terminal, an inverting input terminal, and an output terminal. The non-inverting input terminal of the first operational amplifier is the input terminal of the non-inverting amplifier circuit. The inverting input terminal of the first operational amplifier, one end of the fourth resistor, and one end of the fifth resistor are connected together. The other end of the fifth resistor is grounded. The other end of the fourth resistor is connected to the output terminal of the first operational amplifier, and its connection terminal is the output terminal of the non-inverting amplifier circuit.

7. A weak light signal detection circuit based on electron chopping according to claim 2, characterized in that... The bandpass filter circuit includes a second capacitor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, a second operational amplifier, a third operational amplifier, a fourth operational amplifier, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a twelfth resistor, a thirteenth resistor, and a fourteenth resistor. The second, third, and fourth operational amplifiers each have a non-inverting input terminal, an inverting input terminal, and an output terminal. One end of the second capacitor is the input terminal of the bandpass filter circuit. The other end of the second capacitor is connected to one end of the sixth resistor. The other end of the sixth resistor, one end of the seventh resistor, one end of the third capacitor, and one end of the fourth capacitor are connected together. The other end of the seventh resistor is grounded. The other end of the third capacitor, one end of the eighth resistor, and the inverting input terminal of the second operational amplifier are connected together. The non-inverting input terminal of the second operational amplifier is grounded. The other end of the eighth resistor, the other end of the fourth capacitor, and the output terminal of the second operational amplifier are connected together. The output terminal is connected to one end of the ninth resistor. The other end of the ninth resistor, one end of the tenth resistor, one end of the fifth capacitor, and one end of the sixth capacitor are connected together. The other end of the tenth resistor is grounded. The other end of the fifth capacitor and one end of the eleventh resistor are connected to the inverting input terminal of the third operational amplifier. The non-inverting input terminal of the third operational amplifier is grounded. The other end of the eleventh resistor, the other end of the sixth capacitor, the output terminal of the third operational amplifier, and one end of the twelfth resistor are connected together. The other end of the twelfth resistor, one end of the thirteenth resistor, one end of the seventh capacitor, and one end of the eighth capacitor are connected together. The other end of the thirteenth resistor is grounded. The other end of the seventh capacitor and one end of the fourteenth resistor are connected to the inverting input terminal of the fourth operational amplifier. The non-inverting input terminal of the fourth operational amplifier is grounded. The other end of the fourteenth resistor and the other end of the eighth capacitor are connected to the output terminal of the fourth operational amplifier, and their connection terminals are the output terminals of the bandpass filter circuit.

8. A weak light signal detection circuit based on electron chopping according to claim 2, characterized in that... The phase-sensitive detection circuit includes an inverter circuit and an analog switch. The inverter circuit includes a fifth operational amplifier, a fifteenth resistor, and a sixteenth resistor. The fifth operational amplifier has a non-inverting input terminal, an inverting input terminal, and an output terminal. The analog switch has a first input terminal, a second input terminal, a control terminal, and an output terminal. The first input terminal of the analog switch is connected to one end of the fifteenth resistor, and this connection terminal is the input terminal of the phase-sensitive detection circuit. The other end of the fifteenth resistor and one end of the sixteenth resistor are connected to the inverting input terminal of the fifth operational amplifier. The non-inverting input terminal of the fifth operational amplifier is grounded. The other end of the sixteenth resistor, the output terminal of the fifth operational amplifier, and the second input port of the analog switch are connected. The output terminal of the analog switch is the output terminal of the phase-sensitive detection circuit.

9. A weak light signal detection circuit based on electronic chopping according to claim 2, characterized in that... The low-pass filter circuit includes a seventeenth resistor and a ninth capacitor. One end of the seventeenth resistor is the input terminal of the low-pass filter circuit, and the other end of the seventeenth resistor is connected to one end of the ninth capacitor, with the connection terminal being the output terminal of the low-pass filter circuit. The other end of the ninth capacitor is grounded.

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