The Research On Key Technology Of Readout Circuit Based On Single-photon APD Array Detector

Recently,the requirements of ranging resolution,circuit area and power consumption have been gradually improved in close range laser 3D imaging system.Avalanche photodiode(also called single-photon APD)operating in geiger-mode,has a quick response to a single photon,and its readout circuit features on low noise,so it has a great advantage in high precision large-scale array detection.Based on single-photon APD array detector,two front end unit readout circuits applying to laser ranging in 3D imaging have been designed in this paper.According to the ranging principle of time-of-flight(TOF),the unit circuit consists of active quenching circuit(AQC),time-to-digital converter(TDC)and corresponding timing control circuit.In both two designs,AQC can quench APD in an active way within 1ns,and it realizes an adjustable hold-off time of 3.5-5 ns after quenching.Besides,it can reset APD automatically.In the first design,TDC adopts a two-segment coarse-fine architecture to manage a trade-off between clock frequency and temporal resolution using interpolation technique.The clock frequency has been reduced to 1GHz,which is one fifth of the conventional design frequency.The temporal resolution is 75 ps,and its corresponding ranging resolution is 1.125 cm,achieving a high precision.The circuit area is 95×95?m~2,and the power consumption is 1.08 mW.In the second design,the circuit structure has been enhanced and optimized on the basis of the original design.The clock frequency is 500 MHz,and the temporal resolution is200 ps,indicating a ranging resolution of 3 cm.The circuit area is less than 50×95?m~2,and the power consumption is 0.89 mW,having the advantages of small area and low consumption.The projects have been designed with SMIC 0.18?m 1.8 V CMOS process.Layout post-simulation results show that two schemes can meet their design requirements well.However,there are different degrees of time jitters in both two TDCs.The last part of the paper discusses the causes and provides the corresponding solution.