Research On Key Technologies Of High Precision Time-to-digital Converter

Light Detection and Ranging System is widely used in numerous areas,including obstacle avoidance,measurement,automatic vehicles,and imaging.Especially,LiDAR system has drawn more and more attention due to the rapid development of automatic driving in recent years.The Time-to-Digital system,which is the critical module of the solid-state LiDAR chip,converts the flight time of the laser pulse into digital codes.Thus the system directly determines the precision of LiDAR.A high-performing LiDAR brings growing challenges to Time-to-Digital Converter so that the research on that becomes more and more significant.This thesis focuses on the high precision and high linearity Time-to-Digital Conversion method with its realization.First of all,this thesis establishes a behavioral model for the TDC based on Matlab.Several system errors involving misalignment error,static phase error of the Delay-Locked Loop,and the jitter of the multi-phase clocks are thoroughly studied.The weight of the above errors is compared for the main directions of the optimization and the topic of this thesis.Then,this thesis proposes a new structure named Phase-Error Locked Loop(PELL)and gives a detailed analysis of it.The most remarkable advantage of PELL is the tiny static phase error and reasonable jitter.Simultaneously,the static phase error is not impacted by the PVT variations,which shows the robustness of the structure.Therefore,PELL is perfectly suitable for the TDC.After that,two critical structural issues in the traditional structure of TDC are discussed: the sequential separation of time intervals and the metastability of the sample circuit.A new method called the complementary separation principle based on the united reference is proposed to solve the problem.With this method,the high precision and high linearity of TDC can be ensured without back-ground calibration.According to the above theories,this thesis realizes a multi-channel TDC with the PELL in the smic180 nm CMOS process.The performance of PELL is tested through post-layout simulation,and the results show that the static phase error of this circuit can be limited within 1‰ of the clock period.Meanwhile,the standard deviation of the jitter is around3.07 ps.All these results demonstrate that this PELL can be the appropriate choice for the TDC.Then,a TDC with the complementary separation principle based on the united reference is implemented in the tsmc65 nm process.The measurement results show that this chip has a measurement range up to 2.5 microsecond and the precision of 27.63 ps with1.2V supply voltage and a 200 MHz reference clock.The power consumption of it is 51 mW with a 999 kHz repetition frequency.The INL and DNL of the TDC are ±2.751 LSB and±1.679 LSB,respectively.In summary,The precision and linearity of the proposed TDC is first-class for the LiDAR application.