CN117232666A - Avalanche signal extraction system and method based on single photon detector - Google Patents

Abstract

The invention discloses an avalanche signal extraction system and method based on a single photon detector, wherein the avalanche signal extraction system comprises a double APD balance circuit, a phase-locked loop, a first Butterworth low-pass filter, a small signal tuning amplifier and a second Butterworth low-pass filter which are sequentially connected. The double APD balance circuit outputs an original avalanche signal, the phase-locked loop synchronously locks the frequency of the original avalanche signal and outputs an avalanche signal with single frequency, the first Butterworth low-pass filter filters middle and high frequency noise and outputs a low frequency avalanche signal, the low frequency avalanche signal enters the small signal tuning amplifier to be amplified, the amplified avalanche signal enters the second Butterworth low-pass filter to filter middle and high frequency noise again, and the second Butterworth low-pass filter outputs a stable avalanche signal. The invention makes the intensity of the finally extracted avalanche signal far greater than that of differential noise, can well maintain the waveform of the avalanche signal and remarkably improve the stability of the avalanche signal.

Description

Avalanche signal extraction system and method based on single photon detector

Technical Field

The invention relates to the technical field of single photon detection, in particular to an avalanche signal extraction system and method based on a single photon detector.

Background

Single photon detectors are weak optical signals that detect single photon magnitudes, the principle being that the enhanced sensitivity enables them to detect the smallest energy quantum of light, photons. The single photon detector can count single photons to detect extremely weak target signals, and has wide application in the fields of high-resolution spectrum measurement, nondestructive material analysis, high-speed phenomenon detection, precise analysis, bioluminescence, radiation detection, high-energy physics, spectrum detection, quantum key distribution system and the like. The importance of single photon detector in the field of photoelectron detection makes it one of the important research subjects in photoelectron science in various countries. However, the avalanche signal of the photo-generated carriers is often submerged by the noise of the junction capacitance of the avalanche photodiode, so that the avalanche signal cannot be effectively discriminated.

The extraction of the avalanche signal is generally divided into filtering of the gating differential noise and amplification of the avalanche signal. Common methods for filtering differential noise at present comprise band-stop filtering, low-pass filtering, a capacitance balancing method, a double APD balancing method and the like. The band-stop filter and the low-pass filter can well filter differential noise and achieve good inhibition effect, but the characteristics of fast roll-off and high inhibition ratio of the band-stop filter and the low-pass filter have great damage to avalanche signal waveforms, severe tailing phenomenon and are hardly usable when the gating frequency is low.

The capacitance balancing method has a limited noise suppression performance due to the fact that a fixed capacitance is adopted and is different from an APD junction capacitance in characteristics. The dual APD balancing method is currently the preferred method, however, it requires the use of two APDs with similar characteristics, but only one APD can operate in the optimal state and is costly. While filtering differential noise, weak avalanche signals need to be amplified to be higher than background noise to be effectively identified, and finally the intensity of the extracted avalanche signals is lower than that of the differential noise and unstable.

Therefore, to improve the shortcomings of the prior art, a dual APD balancing method is provided for extracting avalanche signals by mainly using a dual APD balancing circuit.

Disclosure of Invention

The invention aims at solving the defects of the technology and providing a system and a method for extracting avalanche signals based on a single photon detector.

The method is realized by the following technical scheme:

an avalanche signal extraction system based on a single photon detector comprises a double APD balance circuit, a phase-locked loop, a first Butterworth low-pass filter, a small signal tuning amplifier and a second Butterworth low-pass filter which are connected in sequence;

the double APD balance circuit is used for filtering differential noise;

the phase-locked loop is used for outputting a signal with a single frequency;

the first Butterworth low pass filter and the second Butterworth low pass filter are used for filtering medium and high frequency noise;

the small signal tuning amplifier is used for amplifying signals;

the electric pulse signal generated by the gating signal enters the double APD balance circuit, the double APD balance circuit outputs an original avalanche signal, the original avalanche signal enters the phase-locked loop and then is subjected to synchronous locking, the original avalanche signal is subjected to frequency filtering, interference frequency signal processing, and then an avalanche signal with single frequency is output, the avalanche signal with single frequency enters the first Butterworth low-pass filter to filter middle and high frequency noise and then output a low-frequency avalanche signal, and the low-frequency avalanche signal enters the amplified avalanche signal amplified and output by the small-signal tuning amplifier and enters the second Butterworth low-pass filter to filter the middle and high frequency noise again and then output a final avalanche signal.

Further, the double APD balance circuit includes 2 avalanche photodiodes of the same model D1 and D2, respectively, and the avalanche photodiode D1 is connected in parallel with the avalanche photodiode D2.

Further, the small signal tuning amplifier includes a bias circuit and an LC tank, the bias circuit being connected in parallel with the LC tank.

Further, the bias circuit includes a power supply VCC, a bipolar junction transistor U1, a resistor Rb2, a resistor Re, a capacitor Cb, and a capacitor Ce.

Further, one end of a resistor Rb1 of the bias circuit is connected with a power supply VCC, and the other end of the resistor Rb1 is connected with a base electrode of a bipolar junction transistor U1;

one end of the capacitor Cb is used as a connection input signal, and the other end of the capacitor is connected to the base electrode of the bipolar junction transistor U1;

the resistor Rb2 and the resistor Re are connected in parallel and then connected to the emitter of the bipolar junction transistor U1; the capacitor Ce is connected to both ends of the resistor Re in parallel.

Further, the LC tank includes an inductance L1, an inductance L2, a capacitance C1, and a capacitance C2.

Further, an inductance L1 and a capacitance C1 of the LC resonant circuit are connected in parallel; and the capacitor C2 and the inductor L2 are connected in parallel and then connected in parallel with a parallel circuit of the inductor L1 and the capacitor C1 of the LC resonant circuit.

A method for extracting avalanche signal based on a single photon detector, which is applied to the avalanche signal extraction system based on the single photon detector, and comprises the following steps:

step 1: an electric pulse signal generated by the gate control signal enters the double APD balance circuit to filter differential noise in the double APD balance circuit and then output an initial avalanche signal;

step 2: the initial avalanche signal enters the phase-locked loop to filter out a stable avalanche signal with single output frequency of an interference frequency signal;

step 3: the stable avalanche signal enters the first Butterworth low-pass filter to filter the middle-high frequency noise of the stable avalanche signal to obtain a filtered avalanche signal;

step 4: the filtered avalanche signal obtained in the step 3 enters the small signal tuning amplifier to perform frequency selection and amplification treatment on the amplified avalanche signal;

step 5: and the output amplified avalanche signal enters the second Butterworth low-pass filter to be subjected to signal short-term fluctuation filtering treatment, and a final avalanche signal is output.

Further, the frequency of the stable avalanche signal in the step 2 is the same as the frequency of the initial avalanche signal.

The beneficial effects of the invention are as follows:

the system can effectively filter differential noise through the double APD balance circuit and obtain an effective avalanche signal, the frequency of the input signal and the frequency of the output signal can not be greatly changed through the feedback action of the phase-locked loop, the intensity of the extracted avalanche signal is far greater than that of the differential noise finally, the waveform of the avalanche signal can be well maintained, and the stability of the avalanche signal is obviously improved.

Drawings

FIG. 1 is a block diagram of a system architecture of the present invention;

FIG. 2 is a diagram of a dual APD balancing circuit of the present invention;

FIG. 3 is a circuit diagram of a small signal tuned amplifier of the present invention;

fig. 4 is a flow chart of the method of the present invention.

Detailed Description

The present invention will be further described in detail with reference to the following examples, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent, but the scope of the present invention is not limited to the following specific examples.

As shown in fig. 1, an avalanche signal extraction system based on a single photon detector comprises a double APD balance circuit, a phase-locked loop, a first butterworth low-pass filter, a small signal tuning amplifier and a second butterworth low-pass filter which are connected in sequence;

the double APD balance circuit is used for filtering differential noise;

the phase-locked loop filters the interference frequency and outputs a signal with a single frequency;

the first Butterworth low pass filter and the second Butterworth low pass filter are used for filtering medium and high frequency noise;

the small signal tuning amplifier is used for amplifying signals;

the electric pulse signal generated by the gating signal enters the double APD balance circuit, the double APD balance circuit outputs an original avalanche signal, the original avalanche signal enters the phase-locked loop and then synchronously locks the frequency of the original avalanche signal, the phase-locked loop outputs an avalanche signal with single frequency, the avalanche signal with single frequency enters the first Butterworth low-pass filter to filter middle and high frequency noise and then outputs a low-frequency avalanche signal, the low-frequency avalanche signal enters the small-signal tuning amplifier to amplify, and the small-signal tuning amplifier outputs the amplified avalanche signal to enter the second Butterworth low-pass filter to filter middle and high frequency noise again and then output a stable avalanche signal.

The circuit diagram of the double APD balance circuit is shown in fig. 2, and the double APD balance circuit comprises 9 resistors, 5 capacitors and 2 avalanche photodiodes.

The working principle of the double APD balance circuit is as follows:

as shown in fig. 2, the resistor R1 is a debugging resistor, the resistor R4 is a current limiting resistor, the gating signal is connected in series with the protection resistor R1 and the current limiting resistor R4, and the gating signal inputs high-frequency signals to the avalanche photodiodes D1 and D2 of the next stage circuit through the coupling capacitors C3 and C4 respectively. The bias voltages Vb1 and Vb2 are respectively output smoothly through the filter capacitors C1 and C2;

wherein, the electric signal output by the capacitor C3 is input to the cathode of the avalanche diode D1 together with the voltage output by the bias voltage Vb1 through the filter capacitor C1; the signal output by the capacitor C4 is input to the cathode of the avalanche diode D1 together with the voltage output by the bias voltage Vb2 through the filter capacitor C2; for the avalanche diode D1, due to the superposition input of the electric signal and the voltage, the voltage at two ends of the avalanche diode D1 is larger than the breakdown voltage of the avalanche diode, so that an avalanche signal 1 is generated; for the avalanche diode D2, due to the superposition input of the electric signal and the voltage, the voltage across the avalanche diode D2 is larger than the breakdown voltage of the avalanche diode, so that the avalanche signal 2 is also generated; the avalanche signal 1 and the avalanche signal 2 are overlapped to output an original avalanche signal to a phase-locked loop;

the positive electrode of the avalanche diode D1 is connected with the current-limiting resistor R5 and the debugging resistor R7, the positive electrode of the avalanche diode D2 is connected with the current-limiting resistor R6 and the debugging resistor R8, the adjustable transformer T1 is connected with the avalanche diode D1 and the avalanche diode D2 in parallel, and the adjustable transformer T1 is used for controlling the output voltage of the stage of circuit, namely the input voltage of the next stage of circuit;

further, the regulating transformer T1 is connected with the sliding rheostat R9 and the capacitor C5 in parallel, and the parallel circuit outputs an original avalanche signal; the sliding rheostat R9 is used for adjusting the impedance of the circuit, so as to control the voltage across the capacitor C5, namely, balance the output voltage of the circuit.

The double APD balance circuit disclosed by the invention has the following advantages:

(1) The avalanche photodiodes with the same model are adopted, so that the consistency of the capacitance characteristics of the avalanche photodiodes is ensured to the maximum extent, and the possible misoperation caused by manual debugging of the circuit is avoided.

(2) The impedance of the circuit can be adjusted by adjusting the resistance value of the slide rheostat, so that the output voltage of the balance circuit is adjusted.

(3) The balance circuit is designed to make the magnetic fields generated by the currents cancel each other and not to interfere with each other, so that the interference of electromagnetic waves to signals is reduced, and the distortion of the extracted avalanche signals is small.

The original avalanche signal output by the double APD balance circuit enters the phase-locked loop, and the phase-locked loop is a typical feedback control circuit.

The output end of the phase-locked loop is connected with the input end of the Butterworth low-pass filter, and the Butterworth low-pass filter is one of the electronic filters and has the characteristics that the frequency response curve is flat to the maximum extent in a passband, no fluctuation exists, and the band-stop gradually drops to zero. The butterworth filter and also the only filter can keep the same shape of the amplitude versus the frequency curve of the signal regardless of the order. The butterworth low-pass filter is adopted in the invention to filter the middle and high frequency noise by passing the low frequency useful signal, and ensure the smooth form of the signal by eliminating the short-term fluctuation of the signal.

The low-frequency signal output from the Butterworth low-pass filter needs to be further amplified, and the invention adopts the small-signal tuning amplifier to amplify the signal, wherein the small-signal tuning amplifier generally works in a class A state, and can amplify useful signals and inhibit other useless interference signals. In the embodiment, the double-tuned loop amplifier is adopted, and belongs to one of small-signal tuned amplifiers, and the double-tuned loop amplifier has the advantages of amplification, frequency selection, bandwidth and good selectivity.

The small signal tuning amplifier comprises a tuning loop amplifier, and the tuning loop amplifier is adopted in the system, as shown in fig. 2, and comprises a bias circuit and an LC resonance loop, wherein the bias circuit is connected with the LC resonance loop in parallel.

The bias circuit comprises a power supply VCC, a bipolar junction transistor U1, a resistor Rb2, a resistor Re, a capacitor Cb and a capacitor Ce.

One end of a resistor Rb1 of the bias circuit is connected with a power supply VCC, and the other end of the resistor Rb1 is connected with the base electrode of the bipolar junction transistor U1; one end of the capacitor Cb is used as a connection input signal, and the other end of the capacitor is connected to the base electrode of the bipolar junction transistor U1; the resistor Rb2 and the resistor Re are connected in parallel and then connected to the emitter of the bipolar junction transistor U1; the capacitor Ce is connected to both ends of the resistor Re in parallel.

The bias voltage VCC provides power for the circuit, and the resistors Rb1, rb2, re are dc bias resistors for bipolar junction to ensure the amplifying region of the transistor U1. When the bipolar junction ensures that the current at the base of transistor U1 changes, the collector and emitter currents will change by a corresponding factor.

In the double tuned loop amplifier, as shown in fig. 3, the LC tank includes an inductance L1, an inductance L2, a capacitance C1, and a capacitance C2. The inductance L1 and the capacitance C1 of the LC resonant circuit are connected in parallel; and the capacitor C2 and the inductor L2 are connected in parallel and then connected in parallel with a parallel circuit of the inductor L1 and the capacitor C1 of the LC resonant circuit.

When an input signal passes through the LC parallel resonance circuit, a signal with higher frequency generally reaches an output end through the capacitor according to the impedance characteristics of the inductor and the capacitor, and a signal with lower frequency easily reaches the output end through the inductor, namely, the signal is amplified by selecting the frequency, different inhibition effects are achieved on different input frequencies, and further amplified signals with corresponding frequencies are output.

The double-tuned loop amplifying circuit has the advantages that:

(1) Has selectivity; i.e. signals of a certain frequency can be selectively amplified.

(2) A frequency bandwidth; that is, the input signal can be amplified by a plurality of passband bandwidths.

Further, the signal output from the double tuned loop amplifier enters a second butterworth low pass filter, the function of the second butterworth low pass filter is the same as that of the first butterworth low pass filter, the second butterworth low pass filter is used for filtering noise which is not completely filtered or is newly generated in the transmission process, and finally, a stable avalanche signal is output through the second butterworth low pass filter.

As shown in fig. 4, a method for extracting avalanche signals based on a single photon detector is applied to the avalanche signal extraction system based on a single photon detector, the flow chart of the method is shown in fig. 4, and the method comprises the following steps:

step 1: an electric pulse signal generated by the gate control signal enters the double APD balance circuit to filter differential noise in the double APD balance circuit and then output an initial avalanche signal;

step 2: the initial avalanche signal enters the phase-locked loop to synchronously lock the frequency of the original avalanche signal, and the phase-locked loop outputs a stable avalanche signal with single frequency;

the frequency of the single frequency stable avalanche signal is the same as the frequency of the initial avalanche signal in step 1.

Step 3: the single frequency avalanche signal enters the first butterworth low-pass filter; the first Butterworth low-pass filter filters the middle-high frequency noise of the stable avalanche signal and then obtains a filtered avalanche signal;

step 4: the filtered avalanche signal obtained in the step 3 enters the small signal tuning amplifier to perform frequency selection and amplification treatment;

step 5: and 4, enabling the amplified avalanche signal output by the small-signal tuning amplifier to enter the second Butterworth low-pass filter for processing of filtering short-term fluctuation of the signal, and enabling the second Butterworth low-pass filter to output the avalanche signal.

The circuit of the invention comprises a dual APD balancing circuit, a phase locked loop, a first butterworth filter, a small signal tuning amplifier, and a second butterworth filter. The double APD balance circuit can effectively filter noise and can extract useful avalanche signals; after the avalanche signal is extracted, the frequency of the input signal and the frequency of the output signal can be ensured not to change greatly through the feedback action of the phase-locked loop, so that the error is reduced; the signal output by the phase-locked loop can filter out the signals of other useless frequencies through the Butterworth low-pass filter, so that the frequency response curve in the passband is maximally flat; selecting a frequency required by the small signal tuning amplifier and amplifying an input signal; finally, the noise which may not be completely filtered or newly generated in the previous process is filtered by a Butterworth low-pass filter, and finally the avalanche signal which needs to be extracted is obtained.

The invention makes the intensity of the finally extracted avalanche signal far greater than that of differential noise, can well maintain the waveform of the avalanche signal and remarkably improve the stability of the avalanche signal.

Variations and modifications to the above would be obvious to persons skilled in the art to which the invention pertains from the foregoing description and teachings. Therefore, the invention is not limited to the specific embodiments disclosed and described above, but some modifications and changes of the invention should be also included in the scope of the claims of the invention. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not constitute any limitation on the invention.

Claims (9)

1. An avalanche signal extraction system based on a single photon detector is characterized by comprising a double APD balance circuit, a phase-locked loop, a first Butterworth low-pass filter, a small signal tuning amplifier and a second Butterworth low-pass filter which are connected in sequence;

the double APD balance circuit is used for filtering differential noise;

the phase-locked loop is used for outputting a signal with a single frequency;

the first Butterworth low pass filter and the second Butterworth low pass filter are used for filtering medium and high frequency noise;

the small signal tuning amplifier is used for amplifying signals;

and the electric pulse signal generated by the gating signal enters the double APD balance circuit to filter differential noise and output an original avalanche signal, the original avalanche signal enters the phase-locked loop to synchronously lock the original avalanche signal frequency and filter interference frequency signals and then output an avalanche signal with single frequency, the avalanche signal with single frequency enters the first Butterworth low-pass filter to filter middle and high frequency noise and then output a low-frequency avalanche signal, and the low-frequency avalanche signal enters the small-signal tuning amplifier to amplify the signal and output an amplified avalanche signal and enters the second Butterworth low-pass filter to filter the middle and high frequency noise again and then output a final avalanche signal.

2. The avalanche signal extraction system based on a single photon detector according to claim 1, wherein said dual APD balancing circuit comprises 2 identical model avalanche photodiodes D1, D2, said avalanche photodiode D1 being connected in parallel with said avalanche photodiode D2.

3. The avalanche signal extraction system based on a single photon detector according to claim 1, wherein said small signal tuning amplifier comprises a bias circuit and an LC tank, said bias circuit being connected in parallel with said LC tank.

4. The avalanche signal extraction system according to claim 3, wherein said bias circuit comprises a power supply VCC, a bipolar junction transistor U1, a resistor Rb2, a resistor Re, a capacitor Cb, and a capacitor Ce.

5. The avalanche signal extraction system according to claim 4, wherein one end of a resistor Rb1 of said bias circuit is connected to a power supply VCC, and the other end of said resistor Rb1 is connected to a base of a bipolar junction transistor U1;

one end of the capacitor Cb is used as a connection input signal, and the other end of the capacitor is connected to the base electrode of the bipolar junction transistor U1;

the resistor Rb2 and the resistor Re are connected in parallel and then connected to the emitter of the bipolar junction transistor U1; the capacitor Ce is connected to both ends of the resistor Re in parallel.

6. The avalanche signal extraction system according to claim 3, wherein said LC tank comprises an inductance L1, an inductance L2, a capacitance C1 and a capacitance C2.

7. The avalanche signal extraction system according to claim 6, wherein the inductance L1 and the capacitance C1 of the LC tank are connected in parallel; and the capacitor C2 and the inductor L2 are connected in parallel and then connected in parallel with a parallel circuit of the inductor L1 and the capacitor C1 of the LC resonant circuit.

8. A single photon detector based avalanche signal extraction method, characterized in that a single photon detector based avalanche signal extraction system according to any of the claims 1-7 is applied, said method comprising the steps of:

step 1: an electric pulse signal generated by the gate control signal enters the double APD balance circuit to filter differential noise in the double APD balance circuit and then output an initial avalanche signal;

step 2: the initial avalanche signal enters the phase-locked loop to filter out a stable avalanche signal with single output frequency of an interference frequency signal;

step 3: the stable avalanche signal enters the first Butterworth low-pass filter to filter the middle-high frequency noise of the stable avalanche signal to obtain a filtered avalanche signal;

step 4: the filtered avalanche signal obtained in the step 3 enters the small signal tuning amplifier to perform frequency selection and amplification treatment on the amplified avalanche signal;

step 5: and the output amplified avalanche signal enters the second Butterworth low-pass filter to be subjected to signal short-term fluctuation filtering treatment, and a final avalanche signal is output.

9. The method according to claim 8, wherein the frequency of the stable avalanche signal in the step 2 is the same as the frequency of the initial avalanche signal.