Design Of Quenching Circuit For SPAD Applied To Single Photon Counting Detection

Avalanche photodiode is also called Single Photon Avalanche Diode(SPAD)when it is operating in Geiger mode.Under the Geiger mode,SPAD has the characteristic of high gain,low power consumption,small size and so on,also the quick response of single photon signal makes it widely used in single detection system.At present,single photon detection technology is developing towards integrated array,which makes array detection consistency an important design reference.With different breakdown voltages of SPAD array,quenching circuit plays a key role in the performance of single photon detection system as the significant bridge between SPAD and readout circuit.The detection principle of SPAD and its discrete reverse breakdown voltage are discussed in this paper.On account of the breakdown voltage nonuniformity of SPAD array,a quenching circuit with SPAD bias voltage adjustable function is proposed.The proposed circuit utilizes a 4bit DAC to export variable analog voltage to adjust the reset voltage of anode of SPAD dynamically,which can regulate the excess bias voltage uniformly of each SPAD.Through this method,the proposed circuit also can restrain the breakdown voltage nonuniformity phenomenon and realize the purpose of array detection gain consistency.The quenching circuit senses the avalanche current through SPAD junction capacitance and other parasitic capacitance of its anode,which meets the requirement of weak light detection.Meanwhile,gate control mode is adopted to control the hold-off time of single frame during the SPAD Geiger mode,as same as the minimum dead time between adjacent photon signals,which makes sure of circuit working reliability.Quenching circuit with SPAD bias voltage adjustable function is simulated and fabricated using GSMC 0.18?m CMOS process.Both the pre-simulation and the post-simulation reveal that the designed circuit can satisfy the design specification.The measurements of circuit chip indicate that the designed circuit can sense and quench photon signal properly.The single SPAD pixel makes fine adjustment during the reset process(25ns)and make fast quenching process(?3ns).The output voltage range of 4 bit DAC is 0.014V-1.227V,of which the average adjustable step is 80.57mV.The main design targets reach expected goal,which lays the good foundation of the resolution of detection uniformity in SPAD array.