High-Precision GRO-Based ROIC Adopting Sliding Scale Average Method for SPAD Array

Due to the advantages of high sensitivity, fast response speed, and strong interference immunity, the combination of single photon avalanche photodiode (SPAD) and direct time-of-flight (dToF) technology has become the core technology of 3D imaging in laser radar. For the requirements of high-precision dToF ranging and imaging systems, a read-out integrated circuit (ROIC) with pixel-by-pixel time-to-digital converter (TDC) for SPAD array application is implemented with TSMC 0.18lm standard CMOS process in this paper. The high-frequency multi-phase clock that drives the two-segment TDC is provided by the gated ring oscillator (GRO) built in each pixel, and the control voltage of each GRO is stabilized through the closed-loop feedback of the global phase-locked loop (PLL), which reduces the frequency fluctuation of the built-in GRO and achieve high precision requirements. After removing the data from dark counts, this paper adopts the sliding scale technique combined with the average method to realize the effective processing of multi-frame/multiple measurement results and further improve the linearity. The chip measurement results show that the average time resolution and timing range are 124ps and 504ns respectively, and the differential nonlinearity (DNL) / integral nonlinearity (INL) is lower than 0.8 / 1.8 LSB.