An 80 × 60 Flash LiDAR Sensor With In-Pixel Delta-Intensity Quaternary Search Histogramming TDC

• Published in: IEEE journal of solid-state circuits Vol. 57; no. 11; pp. 3200 - 3211
• Main Authors: Park, Seonghyeok, Kim, Bumjun, Han, Su-Hyun, Cho, Jun-Hee, Chun, Jung-Hoon, Choi, Jaehyuk, Kim, Seong-Jin
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.11.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: 3-D imager; CMOS depth sensor; CMOS image sensors; delta intensity; histogramming; Image acquisition; Laser radar; Lidar; light detection and ranging (LiDAR); Luminous intensity; Pixels; quaternary search; Redundancy; Search methods; Sensors; single-photon avalanche diode; Single-photon avalanche diodes; Subframes; time-of-flight (ToF); time-to-digital converter (TDC)
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2022.3202247

This article presents a flash light detection and ranging (LiDAR) sensor featuring an in-pixel histogramming time-to-digital converter (hTDC) based on a delta-intensity quaternary search (DIQS) technique. The proposed 12-b DIQS hTDC is a two-step converter consisting of a 6-b coarse hTDC and a 7-b fine hTDC with 1-b redundancy. The DIQS hTDC synthesizes depth maps with three subframes from the coarse mode and a single subframe from the fine mode, achieving 100-ps resolution without a clock frequency of a few gigahertz. The DIQS repeats dividing the time range of a current step into four periods and finding the location where a target object is placed by comparing the number of events in each period, which is similar to the binary search method but doubles its operating speed. Two time-of-flight (ToF) bits are consecutively determined in every coarse step, and seven ToF bits are estimated by the indirect ToF technique with photon counts. An up-down counter is employed to reduce the memory size by half and enable the delta-intensity technique that can extend the dynamic range by suppressing the uniform background light. The prototype LiDAR with an <inline-formula> <tex-math notation="LaTeX">80\times60 </tex-math></inline-formula> pixel array was fabricated in a 110-nm CMOS image sensor (CIS) process and fully characterized. The maximum detectable range is measured to 45 m with a success rate of 100% at night and 60% under 70-klux background light. The depth accuracy and precision are 2.5 and 1.5 cm from 3 to 4.5 m indoor, respectively, and the precision is maintained to 1.8 cm for the target located at a 1.5-m distance under 60-klux background light. Inherent time-gating and differential signaling of the DIQS hTDC effectively suppress common-mode noise, accomplishing real-time acquisition of depth images with 30 frames/s in a 9-m range at 30-klux background light.