Multievent Histogramming TDC With Pre–Post Weighted Histogramming Filter for CMOS LiDAR Sensors

Abstract

In this study, we have proposed a CMOS light detection and ranging (LiDAR) sensor with high immunity for background noise (BGN) and inter-LiDAR interference (IF). To mitigate pileup distortions that cause signal loss due to large BGN, we implemented multievent weighted histogramming time-to-digital converter (TDC) with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times4$ </tex-math></inline-formula> macro-pixels. The 11-bit two-step TDC and mixed-signal accumulator (MA) were utilized to implement histogramming with area efficiency. To overcome the limited dynamic range of histogram accumulation while preserving the maximum detectable range (MDR), a pre–post weighted histogram filter was implemented to detect only time-correlated time-of-flight (TOF) out of BGN from both sunlight and increased dark noise while enhancing sensitivity through higher excess voltage of single-photon avalanche diodes (SPADs). In addition, the infinite IF canceling (IIC) scheme that employs pulse-position modulation and time-difference modulation was designed to be compatible with the pre–post weighted histogram filter. For the IIC, the ON-chip SPAD-based random number generator provides a random code. A theoretical analysis of LiDAR performance such as MDR was introduced to prove the effectiveness of the pre-post weighted histogram filter. The fabricated sensor demonstrated 8.08-cm accuracy for a range of 32 m under high BGN (105-klx sunlight and 48.72-kcps dark-count rate with increased excess bias voltage) through the pre–post weighted histogram filter and IF immunity through the IIC scheme.