Research On Key Technology Of 320×240 Pixel Multi-mode Lidar Based On SPAD

In recent years,with the rapid development of photoelectric sensing technology and artificial intelligence,Lidar has been more widely used in industrial manufacturing,intelligent transportation,security detection and consumer electronics.Apple’s LIDAR sensor has further introduced photoelectric detection imaging technology to the consumer sector.With the industrial field and miniaturization of electronic target detection requirements are increasing,photoelectric detectors to meet the scene to be measured on the basis of depth information imaging,but also need to have other modes to achieve more detailed and accurate detection or modeling of the scene,such as grayscale information imaging and dynamic target detection imaging,the image of grayscale information imaging can be used as a complement to depth information imaging to detect the reflectance of the object under test,while moving target detection imaging can detect the motion trajectory of the object in the scene to be measured in real time.In this thesis,we focus on the chip-based technology of the receiver side of the multi-mode LIDAR system.The key modules of the LIDAR system are firstly modeled in MATLAB,including the optical system power model,SPAD model and TDC model,and then the pixel cell circuit is studied in depth,and a compact pixel circuit with high fill factor is designed.Finally,a digital column selection circuit with controllable window width is designed,and the functional design of the digital circuit is completed for ranging mode,moving target detection mode and grayscale imaging mode.In this thesis,a pulsed direct time-of-flight lidar chip is implemented based on a 55 nm CMOS process.The lidar chip consists of 320 × 240 pixel cells,480 TDC circuits,a global phase-locked loop,digital column selection circuits with controllable window width,digital circuits for ranging mode,moving target detection mode,and grayscale imaging mode with readout circuits.To increase the frame rate of the chip,320 × 240 pixels are divided into 2 ×160 × 240 pixel units to increase the processing speed of the data inside the chip.The exposure mode of the chip is curtain roll exposure,and the column selection circuit is based on digital circuit to achieve exposure time controllable.Since 320 × 240 pixels can meet the video resolution of QVGA format,the output of the LIDAR chip can be directly imaged on the QVGA screen.The chip has a PW/DNW structure of SPAD with a fill rate of 8.9%to achieve depth detection with a resolution of less than 60 ps within 60 m.The PLL has a bandwidth of 10 M,a frequency division range of 2 to 16,a phase margin of 75°,and a Jitter of 36.6 ps.The lidar chip has three modes:depth imaging,grayscale imaging,and moving target detection,and in the depth information imaging mode is fused into one frame with 100 subframes,which can achieve an imaging frame rate of more than 30fps.The digital output is PISO(200MHz),and the overall plate area is 4351μm × 3025μm.