Research On The Key Techniques Of Multi-channel LiDAR Front-end Chip Based On Circuit Multiplexing

LiDAR is a radar system that acquires target-related information by detecting the scattered light characteristics of a target.Compared with microwave radar,LiDAR has the advantages of high resolution,good concealment,strong anti-interference ability,small size and light weight.It is widely used in the fields of robotics,autonomous driving,unmanned aerial vehicles,meteorological research,three-dimensional urban modeling,and atmospheric environment monitoring.With the development of the Internet of Things and artificial intelligence technology,LiDAR has developed rapidly in the civilian consumer market,especially in the field of autonomous driving,making LiDAR one of the core technologies for researching autonomous driving technology.Domestic research on laser ranging and LiDAR is relatively late,especially the fully integrated LiDAR front-end chip,and most of the domestic and foreign use of discrete quantization devices are not conducive to the integration of the system.Therefore,the thesis will focus on the principle,architecture and circuit implementation of LiDAR front-end multiplexing.The thesis first explains the classification,basic operating principle of the LiDAR and advantages of time domain analog-to-digital converter(ADC).Followed by an analysis of the advantages and disadvantages of the traditional voltage time converter(VTC)and voltage time converter(TDC)structure,introducing the demand for high linearity VTC.Next,it makes a detailed theoretical analysis of the key modules of the front-end chip.For example,the horizontal walking timing discrimination method is applied to reduce the walking error of the system.Finally,the existing noise and non-ideal effects in the system are analyzed from the perspective of signal transmission and processing,such as mismatch of current source and met stability of flip-flop.Also,the corresponding solutions are given in the thesis.For the demanding of autonomous driving,the thesis has completed the principle,architecture,and circuit implementation of the LiDAR front-end circuit reuse.(1)A new type of LiDAR system architecture is proposed to reduce the number of transimpedance amplifier(TIA)and avalanche photodiode(APD)while achieving high resolution and strong background light suppression.(2)TDC/ADC multiplexing technology is proposed.The feasibility of multiplexing is analyzed through the principle and working timing of pulsed LiDAR.TDC circuit multiplexing is realized,which reduces the overall power consumption of the quantization system and improves the radar system stability and reliability.(3)A low-noise,low-power transimpedance amplifier is designed.It adopts a three-level inverter structure and dual power supply,achieving an average input reference noise of 1.2 pA/(?)with low power consumption and guaranteed output swing.(4)A high linearity voltage-to-time converter is proposed.It based on the principles of sampling and constant current source charging to achieve high linearity.The simulation results show that the VTC's SFDR reaches 68 dB within the 600mV differential input range.Even considering the PVT effect,the SFDR of the VTC can reach 59 dB,which is more robust.(5)A high-precision time-to-digital converter is designed.It uses a ring oscillator-based pseudo-differential structure and interpolation technology to achieve a 6.25 ps time accuracy and a detection accuracy of millimeter level.In addition,the TDC has a natural dynamic element matching characteristics,reducing the impact of component mismatch and improving the linearity of TDC.The prototype is fabricated in TSMC 65nm standard CMOS technology,including an ADC and eight-channel TIA.The entire chip area is 1.4×0.8 mm2,and the chip power consumption is 29.28 mW.Measured results show that TIA achieves high and low gains of 82 dB? and 47 dB?,corresponding average input reference noises are 41.9 pA/(?)and 2.5 pA/(?),respectively,and the dynamic range reaches 80 dB;at a sampling rate of 500MS/s,the ADC reaches SNDR of 47 dB and SFDR of 56 dB;at 70 klux solar light intensity and 6.16 mW average laser emission power,the system detection distance reaches 60 m and the detection error is less than 0.1%.