A 100 x 80 Flash LiDAR Sensor With In-Pixel Zoom-Histogramming TDC and Self-Referenced Single-Slope ADC Based on Analog Counters

Abstract

This article presents a CMOS flash light detection and ranging (LiDAR) sensor featuring an in-pixel histogramming time-to-digital converter (hTDC) with a minimal footprint of 1110 mu m(2) facilitated by analog counters. The proposed hTDC utilizes a two-step approach to combine a coarse step using the successive approximation (SA) method and a fine step based on phase-delay calculation akin to the indirect ToF (iToF) technique, achieving a resolution of 200 ps. Compared to the conventional digital counters, the proposed analog counter replaced with histogram memories attains a substantial power reduction of 3300-fold under 80-klx illumination. The analog counter consumes only 8 nW for in-pixel histogramming operation and occupies 6.5% of the hTDC area. Furthermore, an in-pixel self-referenced single-slope analog-to-digital converter (SS-ADC) is devised to mitigate the vulnerability of the analog counter to PVT variations. This SS-ADC can suppress the pixel-to-pixel gain variation, suppressing the non-uniformities of counters. The timing generator (TG) of each pixel, which originally generates the time gate window, has been reconfigured to serve as a 10-bit counter for A/D conversion. The prototype LiDAR sensor with a 100 ${\times }$ 80 pixel array was fabricated in a 0.11- $\mu $ m CMOS image sensor (CIS) process. The coarse TDC has a resolution of 75 cm and can achieve a detection range of up to 24 m with less than one LSB error over all measurements. Under indoor conditions, the coarse and fine TDC measures the depth accuracy and precision of 4.8 and 2.8 cm, respectively, within the 6-7.5-m range.