Research On FPA Readout Circuit Of APD 3D LIDAR

In recent years,with the development of autopilot,sensing,missile tracking and other civil and military fields,the market is demanding more and more for the real-time imaging,dynamic perception and shape resolution of radar,so it is more and more difficult for the common LADAR to meet the requirements.Compared with ordinary LADAR,APD 3D LADAR can obtain the intensity information and depth information of the target object at the same time,and it is easy to distinguish the shape of the object and track the movement track,which has been gradually applied in various fields.For the APD LADAR system,the focal plane array readout circuit is the most important module,which is responsible for the processing of the target signal and determines the performance of the system.At present,APD 3D LADAR focal plane array readout circuit lacks an optoelectronic integration design scheme,and the optoelectronic conversion characteristics of APD have been neglected by circuit designers,which may result in the mismatch between the designed readout circuit and the optical front end.Firstly,the research status and development trend of APD 3D LADAR array FPA readout circuit is introduced and analyzed.Secondly,the parameters of APD and the working principle and parameters of the 3D lidar system are analyzed in detail,and the system parameters are decomposed into APD and circuit levels to provide guidance for subsequent model establishment and circuit design.Thirdly,according to APD parameters and the physical process of photoelectric conversion,the photoelectric integration model is established to guide the readout circuit design.Then,the readout circuit of focal plane array pixel is analyzed and designed in detail to improve the precision and reduce the delay respectively from the signal amplifier module,comparator module and TDC module.Finally,a correction scheme for walking error and non-uniformity is proposed to solve the problem of system error caused by walking error and non-uniformity.The main work and innovations are as follows:(1)The physical basis of the photoelectric conversion characteristics of SACM APD is analyzed in detail,and the carrier variation equations of anode,cathode,absorption area and multiplication area are derived.Then,the circuit models of four areas of APD and photoelectric integration model are established based on PSpice,and the dark current,photocurrent and pulse response characteristics of APD are given,which provides a view of photoelectric integration design for subsequent circuit design.(2)Based on APD photoelectric integration model,the structure of APD focal plane pixel readout circuit is analyzed and designed in detail,the overall design scheme is given,and the signal amplification structure,comparator structure and TDC structure are analyzed and designed respectively.The signal amplification structure completes the acquisition of the intensity signal and has good linearity;The comparator adopts threestage structure to realize 5.71 ns flip delay and reduce the overall delay of the system.TDC adopts two-stage structure to complete the acquisition of depth signal and meet the design accuracy requirement of 0.5ns.(3)The walking error of comparator can be reduced from 3.4ns to 0.4ns,and walking error of pixels output can be reduced from 3.2ns to 0.8ns.The non-uniformity between pixels is deduced from the view of photoelectric integration,and the correction scheme is proposed.