Design And Implementation Of APD Array Detector Readout Circuit

Avalanche Photon Diode,as a new type of photodetector,has been widely used in laser ranging imaging,optical communication and other fields.Geiger-mode Avalanche Photon Diode detector,which works in Geiger-mode,has the ability of single photon detection and can output digital pulse signal directly.It has the advantages of high detection efficiency,small size and convenient maintenance.The readout circuit plays a vital role as a bridge between the single photon detector and the subsequent imaging system.However,with the increasing scale of APD array detector,the negative influence of parasitic effect and noise interference of APD array detector on readout circuit becomes more and more serious,which leads to the increase of design complexity and cost of readout circuit,and severely limits the application of APD array detector.Therefore,in this thesis,the readout circuit of GM-APD array detector is designed on the basis of studying the working principle of GM-APD array detector,aiming at the problems of long quenching time and low ranging accuracy.The main research contents and results of this thesis are as follows:1)Based on the working principle of the GM-APD array detector laser ranging imaging system,the architecture and timing of the readout circuit system are designed.Research and analysis of electrical model of GM-APD detector combined with passive quenching circuit.2)Aiming at the problems of long quench time and slow response speed of the readout circuit of the GM-APD array detector,a design method of an avalanche signal detection unit is proposed.It mainly includes: a capacitor quenching circuit structure is proposed to effectively reduce the dead time of the quenching circuit.According to the working characteristics of the GM-APD detector,the avalanche signal amplifier circuit,identification and shaping circuit and pulse trigger circuit are designed,and the simulation is verified by Multisim software.3)Aiming at the problems of low measurement accuracy and large ranging error of the readout circuit of the GM-APD array detector,a design scheme of a time-to-digital conversion unit is given.Based on the FPGA development platform,on the basis of studying the principle of time interval measurement,the method of combining coarse count and fine count is determined to carry out the design.The coarse counting module is realized by direct counting method,while the fine counting module is realized by tap delay chain,which is verified by Modelsim software to measure the time interval to be tested.4)An experimental platform for the laser ranging system of the GM-APD array detector is set up,and the designed readout circuit is experimentally verified.The results show that the quenching time of the readout circuit designed in this thesis is 18 ns,the resolution of the time-to-digital conversion unit is 125 ps,the measurement accuracy is between 0.20LSB-0.70 LSB,the ranging range is between 30cm-2km,and the actual5)ranging error is less than 45 cm,which provides a good foundation for the design of readout circuit of large-scale fully integrated focal plane array detector.