Design And Implementation Of A Self-Calibrating TDC Digital Circuit For TOF Measurement

With the rapid development of the smart car industry,Li DAR,as a combination of radar technology and laser technology,has the advantages of high resolution,strong anti-interference ability,and small size in long-distance environmental perception,and has significant advantages in market-oriented products.TDC is usually used to measure the time interval between the round-trip pulses of the laser between the target and the lidar receiver-known as TOF.TDC is the core functional component used for timing in lidar,and its resolution,dynamic range,linearity and stability and other parameters will directly affect the accuracy of lidar ranging.Therefore,it is of great significance to conduct in-depth research on the time-to-digital converter circuit applied to lidar time-of-flight measurement.In order to comply with the development trend of high precision and digitization of time-to-digital converters,in-depth and meticulous research on time-to-digital converters has been carried out.In order to realize a time-to-digital converter with large dynamic range and high time measurement resolution,which can be applied to lidar time-of-flight measurement,a self-calibrating TDC chip for TOF measurement was designed and implemented based on0.18μm CMOS process.The main research contents and innovations of this paper are as follows:(1)According to the application requirements of lidar time-of-flight measurement,the overall architecture of the time-to-digital converter is proposed and designed.It is improved on the basis of the circular delay line architecture and adopts a three-level counting structure.In the case of 60.8ps time resolution,the maximum dynamic range can reach 8ms,with high measurement accuracy and large dynamic range.(2)Aiming at the problem that the measurement resolution will fluctuate due to the unit delay change and the influence of the external environment,a real-time resolution calibration algorithm is designed.By calibrating the internal clock output from the circular delay line by an external precise reference clock after each measurement,the microcontroller calculates the real-time resolution of each measurement based on the calibration results.This algorithm can reduce measurement errors caused by factors such as environment and noise.(3)For the case where real-time resolution is not required,a simple algorithm for the measurement results is proposed.The microcontroller replaces the measurement results by reading the time-of-flight calibration offset,which is used to simplify the calculation steps of the measurement results in the microcontroller.(4)Due to the existence of factors such as circuit delay,the integer and fractional two-level counters have the problem of asynchronous.Based on this problem,the cause of the error is analyzed.According to the results of the two counters and the control signal,a decoding circuit with compensation function is designed to correct the error caused by the delay.Based on the proposed main functions,the system architecture,workflow,and resolution real-time calibration algorithms and simple algorithms for measurement are defined.The core measurement structure TDC-CORE,decoding module,state control module,control register module and dedicated SPI interface are designed and simulated.Functional simulation,FPGA verification,synthesis,formal verification and layout design of the overall circuit are carried out.The layout area is 980×800μm~2,the maximum operating current is2m A,and the power consumption is about 3.6mW.