CN104677511B - A kind of single photon counting discriminator circuit with threshold values automatic control function - Google Patents

Abstract

The single photon counting discriminator circuit with threshold automatic control function of the present invention comprises: resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, rheostat W1, capacitor C1, capacitor C2, capacitor C3, capacitor C4, capacitor C5 , Capacitor C6, diode D1, comparator IC1 and operational amplifier IC2. Resistor R1, resistor R3, capacitor C1, capacitor C4, capacitor C5, capacitor C6, comparator IC1 and rheostat W1 form a comparator with adjustable threshold. Resistor R2, resistor R4, resistor R5, diode D1, capacitor C2, capacitor C3 and operational amplifier IC2 form an integral circuit for dynamically adjusting the comparison threshold of the comparator. The invention utilizes an integral circuit to integrate the noise touch pulse output by the discriminator, and dynamically adjusts the comparison threshold of the comparator in real time according to the integral value, so that the system can obtain the best detection sensitivity. The invention has the advantages of simple structure, low cost, low power consumption, good real-time controllability and the like, and can effectively reduce the influence of system environment changes.

Description

A Single Photon Counting Discriminator Circuit with Automatic Threshold Control Function

technical field

The invention relates to a single photon counting discriminator circuit with threshold automatic control function.

Background technique

Single photon detection technology is a kind of extremely weak light detection technology. It has a wide range of applications in sensory fields. The photoelectric receiving devices used in single photon detection technology mainly include photomultiplier tubes, avalanche photodiodes and superconducting nanowire single photon detection devices. In single-photon detection systems using these photoelectric receiving devices, noise pulses will generate false counts, which will affect the detection sensitivity of the system. The false counts of single-photon detection systems mainly come from dark counts and post-pulse counts. Dark counts mainly come from thermal excitation, tunnel penetration and potential wells at doping defects. Thermal excitation will cause electrons to transition from full band to empty band, and at the same time, holes will be generated in the full band. After these electron holes are multiplied by avalanche , will produce false counts, the so-called dark counts. The post-pulse is related to the signal photon. Since the potential well is formed at the doping defect of the optoelectronic device, the potential well captures the carrier during the avalanche signal and releases it in the subsequent time. When the next avalanche voltage pulse is triggered, the avalanche signal may be triggered. cause false counts.

For post-pulse counting, the system can eliminate it by increasing the trigger interval of the avalanche pulse voltage. When the trigger interval of the avalanche pulse voltage should be large enough (more than a few µs), the impact of post-pulse counting is very small, and the pseudo-counting of the system mainly depends on Counting in the dark. The traditional method to reduce the dark count is mainly to reduce the temperature of the photoelectric device by cooling technology, but this will undoubtedly increase the power consumption, cost and volume of the system. Another method is to obtain the optimal dark count pulse generation rate by setting a fixed optimal comparison threshold for the discriminator circuit in the single-photon detection system to obtain the optimal detection sensitivity. However, since the dark noise state of the system will change with the change of the environmental conditions, it means that the comparison threshold must also be adjusted in real time according to different noise states. Therefore, the fixed threshold method obviously cannot meet this requirement. .

Contents of the invention

The purpose of the present invention is to provide a single photon counting discriminator circuit with simple structure, low cost and automatic threshold value control function.

The single photon counting discriminator circuit with threshold automatic control function of the present invention comprises: resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, rheostat W1, capacitor C1, capacitor C2, capacitor C3, capacitor C4, capacitor C5, capacitor C6, diode D1, comparator IC1 and operational amplifier IC2; one end of capacitor C5 is the input end, the other end is connected to the positive phase end of comparator IC1, and the end of capacitor C1 and capacitor C4 connected in parallel is connected to comparator IC1 The power supply end and one end of the resistor R1 are connected to the DC power supply together, the other end of the parallel connection of the capacitor C1 and the capacitor C4 is connected to the ground, the other end of the resistor R1 is connected to one end of the rheostat W1, the variable end of the rheostat W1, one end of the capacitor C6 and the resistor One end of R5 is connected and then connected to the inverting end of comparator IC1, the other end of rheostat W1, the other end of capacitor C6 and the ground end of comparator IC1 are connected to ground, and one end of resistor R3 is compared with one end of resistor R2 The other end of the resistor R3 is the output end, the other end of the resistor R2 is connected to the positive phase end of the diode D1, the parallel connection of the resistor R4 and the capacitor C2 is connected to the inverting end of the diode D1 and the operational amplifier IC2 The positive phase end of the resistor R4 is connected to the parallel connection of the capacitor C2, the other end of the capacitor C3 and the ground terminal of the operational amplifier IC2 are all connected to the ground, the inverting terminal of the operational amplifier IC2 is connected to the output terminal of the operational amplifier IC2 and the resistor The other end of R5 is connected, and the other end of the capacitor C3 is connected to the power supply end of the operational amplifier IC2 and then connected to the DC power supply.

The beneficial effects of the present invention are:

The single photon counting discriminator circuit with threshold automatic control function of the present invention uses a suitable integral circuit to integrate the noise counting pulses output by the discriminator, and dynamically adjusts the comparison threshold of the discriminator in real time according to the integral value, thereby Make the system get the best signal-to-noise ratio. Compared with the traditional refrigeration technology, the present invention has the advantages of simple structure, low cost, and low power consumption; compared with the traditional fixed threshold method, the circuit of the present invention has good real-time controllability and can effectively reduce the influence of system environment changes , so that the system can obtain the best detection sensitivity. In the case of harsh detection environment and high noise count ratio, the effect of the invention is particularly remarkable.

Description of drawings

Fig. 1 is a circuit schematic diagram of a single photon counting discriminator with automatic threshold control function of the present invention.

Fig. 2 is a schematic block diagram of the application of the present invention in a single photon detector system.

detailed description

Further illustrate the present invention below in conjunction with accompanying drawing.

With reference to Fig. 1, the single photon counting discriminator circuit with threshold automatic control function of the present invention comprises: resistance R1, resistance R2, resistance R3, resistance R4, resistance R5, rheostat W1, electric capacity C1, electric capacity C2, electric capacity C3, electric capacity C4, capacitor C5, capacitor C6, diode D1, comparator IC1 and operational amplifier IC2; one end of capacitor C5 is the input terminal IN, the other end is connected to the positive phase end of comparator IC1, and one end of capacitor C1 and capacitor C4 is connected in parallel The power supply end of the comparator IC1 and one end of the resistor R1 are connected to the DC power supply Vcc, the other end of the parallel connection of the capacitor C1 and the capacitor C4 is connected to the ground, the other end of the resistor R1 is connected to one end of the rheostat W1, the variable end of the rheostat W1, One end of the capacitor C6 and one end of the resistor R5 are connected to the inverting end of the comparator IC1, the other end of the rheostat W1, the other end of the capacitor C6 and the grounding end of the comparator IC1 are connected to the ground, and one end of the resistor R3 is connected to the ground. One end of the resistor R2 is connected to the output end of the comparator IC1, the other end of the resistor R3 is the output end OUT, the other end of the resistor R2 is connected to the positive phase end of the diode D1, the end of the parallel connection of the resistor R4 and the capacitor C2 is connected to the output end of the diode D1 The inverting terminal is connected to the non-inverting terminal of the operational amplifier IC2, the other end of the parallel connection of the resistor R4 and the capacitor C2, one end of the capacitor C3 and the ground terminal of the operational amplifier IC2 are connected to the ground, and the inverting terminal of the operational amplifier IC2 is connected to the operational amplifier The output end of IC2 is connected to the other end of the resistor R5, and the other end of the capacitor C3 is connected to the power supply end of the operational amplifier IC2 and then connected to the DC power supply Vcc.

In Figure 1, IN is the signal input terminal, which is connected to the output terminal of the amplifier of the single photon detection system when in use. Capacitor C5 is a DC blocking capacitor for isolating DC signals. Resistor R1 and rheostat W1 form a voltage divider network to provide an adjustable initial comparison voltage for the inverting output terminal of comparator IC1. Capacitor C6 is used to filter out the AC signal at the inverting terminal of comparator IC1. The parallel network composed of capacitor C1 and capacitor C4 mainly provides a good AC ground channel for the power supply terminal of the comparator to prevent ground bounce signal and other noise interference. Resistor R3 acts as an output isolation resistor for the comparator. When in use, the output terminal OUT needs to be connected to the counter input terminal in the single photon detection system. Resistor R2, diode D1, capacitor C2, resistor R4 and operational amplifier IC2 form an integral circuit, which can integrate the counting trigger pulse signal output by comparator IC2, and output a voltage value related to the noise pulse generation rate. Send it to the inverting terminal of comparator IC1 through matching resistor R5, so as to change the comparison threshold voltage Vc of the inverting terminal of comparator IC1 in real time, so that the discriminator outputs an optimal noise pulse generation rate, so that the system can obtain the best detection sensitivity . Operational amplifier IC2 forms a follower, which mainly plays a buffer role. Capacitor C3 mainly provides a good AC grounding path for the power supply end of the follower to prevent ground bouncing signals and other noise interference.

Comparator IC1 can use high-speed integrated comparators, such as MAX9600, MAX913 produced by Maxim, etc., and the appropriate model can be selected according to the speed response requirements of the entire system. Operational amplifier IC2 can be a high-speed operational amplifier, such as LMH6624 produced by National Company, or the model with the best cost performance can be selected according to the operating frequency requirements of the single photon detection system. Diode D1 adopts fast Schottky diode, such as MUR160 and so on. Capacitor C2 should be a high-speed ceramic capacitor with high stability and low distribution parameters. Capacitors C1 and C3 should be high-speed ceramic capacitors with low distribution parameters, and the value is about 0.1µF. They can also be replaced by multiple high-speed ceramic capacitors connected in parallel. Capacitor C4 should be a tantalum capacitor with a value of about 10µF. The value of the DC power supply Vcc can vary depending on the integrated circuit used, generally 3.3V or 5V. In order to reduce the impact of distributed inductance of the device, the devices used should be packaged in small-sized surface mount packages as much as possible. When making printed circuit boards, in order to reduce the influence of circuit board distribution parameters as little as possible, the printed circuit board should be designed according to the principle of fast circuit design, such as: the layout of components should be as compact as possible, the leads between devices should be as short as possible, and the Large areas of ground, etc.

The working principle of the single photon counting discriminator circuit with threshold automatic control function of the present invention will be further described below in conjunction with FIG. 2 . Figure 2 is a single-photon detection system using an avalanche photodiode. In order to increase the avalanche gain of the avalanche diode and improve the detection sensitivity, the avalanche photodiode APD of the system is in Geiger mode (Geiger mode), that is, reverse bias operating at voltages above the avalanche voltage. When the bias voltage is higher than the avalanche voltage, an effective single photon will trigger the APD to generate an avalanche signal. In order to detect the next photon, the bias voltage must be reduced below the avalanche voltage to restore the avalanche diode to its initial state. This working mode can not only improve the lifetime of the avalanche diode, but also effectively reduce the dark count. In the system in Figure 2, when the effective single photon does not arrive, the bias voltage of the APD is provided by the DC bias voltage, which is lower than the avalanche voltage of the APD, and the APD is in the initial state of low sensitivity. When an effective single photon arrives, the computer control system CPU sends a trigger signal to the pulse bias voltage, and the trigger pulse bias voltage sends a pulse voltage to the APD, so that the APD is in a state of over-avalanche voltage, so that the APD is triggered by an effective single photon. Generate an avalanche pulse signal, the avalanche pulse signal is amplified by the amplifier, and sent to the positive phase terminal of the comparator IC1, so that the comparator outputs a digital count trigger pulse signal and sent to the counter through the resistor R3, and the counter triggers each received count The pulses are accumulated and counted and the final result is sent to the CPU. The CPU divides the final accumulated count value of the counter by the total number of avalanche triggers to obtain the capture probability of effective photons and analyze the measurement results according to the probability. In the system shown in Figure 2, resistor R2, diode D1, capacitor C2, resistor R4, and operational amplifier IC2 form an integral circuit, which can integrate the counting trigger pulse signal output by comparator IC2, and output and noise pulse occurrence rate When the noise pulse generation rate is too large, the voltage value output by the integrator is also large, so that the comparison threshold voltage Vc of the inverting terminal of the comparator IC1 also becomes larger, thereby suppressing the change of the noise pulse generation rate big. Conversely, when the noise pulse generation rate is too small, the output voltage value of the integrator becomes smaller, so that the comparison threshold voltage Vc at the inverting terminal of the comparator IC1 also becomes smaller, so that more effective single-photon signal pulses can pass through. The integrator enables the system to overcome the influence of environmental changes and obtain the best detection sensitivity by adjusting the comparison threshold of the comparator in real time. The effect of the discriminator circuit of the invention is particularly remarkable when the detection environment of the system is harsh and the noise count ratio is high.

In the integral circuit composed of resistor R2, diode D1, capacitor C2, resistor R4, and operational amplifier IC2, resistor R2, diode D1, and capacitor C2 form a charging circuit, and its charging time constant is about R2×C2. Capacitor C2 and resistor R4 A discharge circuit is formed, and its discharge time constant is R4×C2. In order to make the comparison threshold Vc of the comparator IC1 obtain an optimal dynamic value. The correct value of charge constant and discharge constant is very important. Usually, the charge constant should be much lower than the discharge constant. The ratio should depend on the system conditions. If the typical pulse width of the noise pulse is about 30ns, compared to the best detection sensitivity , The average time interval of noise pulse generation is about 4ms, and the ratio of discharge constant to charge constant is about 150.

Claims (1)

1. A single photon counting discriminator circuit with threshold automatic control function is characterized in that it comprises: resistance R1, resistance R2, resistance R3, resistance R4, resistance R5, rheostat W1, electric capacity C1, electric capacity C2, electric capacity C3, Capacitor C4, capacitor C5, capacitor C6, diode D1, comparator IC1 and operational amplifier IC2; one end of capacitor C5 is the input terminal IN, the other end is connected to the positive phase end of comparator IC1, and the end of capacitor C1 and capacitor C4 are connected in parallel The power supply end of the comparator IC1 and one end of the resistor R1 are connected to the DC power supply Vcc, the other end of the parallel connection of the capacitor C1 and the capacitor C4 is connected to the ground, the other end of the resistor R1 is connected to one end of the rheostat W1, the variable end of the rheostat W1, One end of the capacitor C6 and one end of the resistor R5 are connected to the inverting end of the comparator IC1, the other end of the rheostat W1, the other end of the capacitor C6 and the grounding end of the comparator IC1 are connected to the ground, and one end of the resistor R3 is connected to the ground. One end of the resistor R2 is connected to the output end of the comparator IC1, the other end of the resistor R3 is the output end OUT, the other end of the resistor R2 is connected to the positive phase end of the diode D1, the end of the parallel connection of the resistor R4 and the capacitor C2 is connected to the output end of the diode D1 The inverting terminal is connected to the non-inverting terminal of the operational amplifier IC2, the other end of the parallel connection of the resistor R4 and the capacitor C2, one end of the capacitor C3 and the ground terminal of the operational amplifier IC2 are connected to the ground, and the inverting terminal of the operational amplifier IC2 is connected to the operational amplifier The output end of IC2 is connected to the other end of the resistor R5, and the other end of the capacitor C3 is connected to the power supply end of the operational amplifier IC2 and then connected to the DC power supply Vcc.