Design And Study Of The Noise Reduction System For Single Photon Avalanche Diode

Single photon avalanche diode(SPAD)is widely used in laser ranging,lidar,quantum key distribution,medical imaging,fluorescence lifetime detection and other fields because of its high gain.The noise of SPAD is mainly divided into dark count and afterpulse,the dark count is randomly distributed,and the afterpulse is caused by the front pulse and correlated with the front pulse in time domain.High dark count and afterpulsing will limit the signal-to-noise ratio and detection sensitivity of the single photon detection system based on SPAD,and increase the bit error rate of the system.In order to limit the afterpulsing effect,a real-time afterpulsing correction system for SPAD is designed based on the characteristics of afterpulsing.The system has a simple structure and is suitable for any SPAD of structure and working voltage.The system consists of a passive quenching readout circuit and a afterpulsing correction circuit.The SPAD output avalanche event is output to the afterpulsing correction circuit through the passive quenching readout circuit.A time interval threshold is set in the afterpulsing correction circuit to determine whether the afterpulsing effect occurs.When the time interval between two adjacent avalanche pulses is greater than the set time interval threshold,the afterpulsing correction module combines two avalanche pulses into one pulse to limit the afterpulsing effect.The experimental results show that the afterpulsing correction system can reduce the afterpulsing probability of a planar SPAD with an operating voltage of 26V from 4.0%to less than 0.5%,and another commercial reach-through SPAD with an operating voltage of 126V from 3.84%to less than 0.4%after afterpulsing correction.The noise reduction system of SPAD based on metal layer masking is a SAPD array system based on 0.18um CMOS process.A specific SPAD is selected in the array to use metal layer masking to make it only output dark count.The output of metal masked SPAD can be used to reduce the dark count of other SPAD outputs in the array.In addition,the breakdown voltage and the temperature of the array can be monitored in real time by analyzing the output of metal masked SPAD.The experimental results show that the breakdown voltage of the designed SPAD is 13V and can detect visible light in the range of450nm～850nm.The maxima photon detection probability and time jitter are 35%and176ps respectively with the overvoltage(the part that exceeds the breakdown voltage)of3V.Without dark count rate correction,the dark count rate of SPAD is 1.38 counts/s·μm~2with overvoltage of 1V and 14.62 counts/s·μm~2with overvoltage of 3V.After the dark count rate correction,nearly 90%of the dark count rate is eliminated,and the dark count rate of SPAD is 1.68 counts/s·μm~2with overvoltage of 3V.The breakdown voltage and temperature of other SPAD in the same array can be obtained by monitoring the dark count rate of metal mask SPAD.In addition,the afterpulsing effect of SPAD,the crosstalk between SPAD in the array and the influence of preparation process on the performance of SPAD are also analyzed.