Research And Design Of A Pixel-level Time-to-digital Converter

Time interval quantification technology has important significance in radar imaging,laser ranging,and medical image scanning.In order to obtain precise time,more and more research teams are researching Time-to-Digital Converters(TDC)and Time-Amplitude Converter(TAC).The traditional TDC generally uses units to delay the propagation time and adopts the all-digital circuit for research and design.The TDC can have high precision wide dynamic range and high integration.However TDC needs to use a high-frequency reference clock,which has high interference with the on-chip analog circuit.And TAC is based on the ramp signal,and its signal is analog.TAC does not interfere with the analog front-end circuit.TAC can also achieve high levels of integration and accuracy.But TAC has a trade-off between dynamic range and accuracy which limites the range of applications.This paper presents two time interval quantization techniques,which are the in-pixel TDC design for APD array readout circuits and the design of a digital-assistant time-toamplitude converter(DATAC).Both design schemes are based on the traditional two-step architecture.Quantization is performed by combining fine and course counting.The coarse counting part is completed by the counter.Both designs are based on a 0.18?m CMOS process.The fine counting part of the TDC in the readout circuit of the APD array is completed by a delay chain constructed of the delay unit in the standard cell library.The resolution is the delay time of the delay unit.The test result shows that the time resolution is 1ns and the dynamic range is 4?s.The DATAC samples the triangular wave signal to achieve fine quantization.The simulation results show that the gain is 500ps/5mV.And the ADC can achieve a dynamic range of 10?s.The resolution of DATAC is 500ps.