Design Of Gain Uniformity Control Circuit For Current Mode Linear Array SPAD

Avalanche photodiode(APD)operating in Geiger Mode(GM),known as Single Photon Avalanche Diode(SPAD),has the ability to detect a single photon.SPAD is widely applied in laser radar 3D imaging,quantum encryption,fluorescence lifetime detection and other fields due to its merits of rapid detection,convenient practicality and high integration.In recent years,SPAD has developed toward array type and integration.However,problem of gain non-uniformity of array SPAD has become a technical bottleneck restricting its development.According to the physical characteristics of SPAD and the inconsistency of SPAD gain caused by technology,a linear SPAD gain uniformity control circuit based on current mode is designed.In this mode,the specific working state of the detector is determined by controlling the current flow through the SPAD detector.A 4 bit bias current is used to generate a configurable reference current,and the reference current is copied to each pixel through a current mirror.Even if the reverse bias voltage of each SPAD detector is different,it can work under the same bias current.That is to say,each detector can match the bias current by adaptively adjusting its anode potential,thus eliminating the array SPAD under a fixed reverse bias voltage.The nonuniform detection sensitivity due to different reverse breakdown voltages significantly improves the consistency of SPAD gain and sensitivity of linear array.At the same time,aiming at the new problem that the quenching time of current-biased SPAD is not uniform due to the inconsistency of the reverse bias point,a quenching circuit for detecting and controlling the change rate of the anode voltage of SPAD is proposed,which can reduce the quenching time and eliminate the excessive difference of the quenching time of each pixel.Based on TSMC 0.35?m COMS technology,the design simulation and chip verification of current mode linear SPAD gain uniformity control circuit are completed in this thesis.The simulation results show that the designed bias current generator can generate bias current in the range of 100 nA to 1600 nA,and the relative error of adjusting step size is less than 3.5%.In the quenching circuit designed to detect the change rate of SPAD anode voltage,the quenching time is less than 12.2ns,and the detection delay is less than 8.5ns.The overall performance meets the design requirements.The chip test results show that compared with the free mode,the standard deviation of dark counting for different pixels of SPAD with current regulation mode is reduced by more than half,which indicates that the gain uniformity of detector array is improved significantly.