A 64 × 64 SPAD-Based Indirect Time-of-Flight Image Sensor with 2-Tap Analog Pulse Counters

Byungchoul Park, Injun Park, Chanmin Park, Woojun Choi, Yoondeok Na, Myung Jae Lee, Youngcheol Chae

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


This article presents a 64 × 64 indirect time-of-flight (iToF) image sensor with a depth range of 50 m, integrated into a 1P4M 110-nm CMOS process. The sensor is based on a single-photon avalanche diode (SPAD), the range-dependent phase delay of which is measured by compact analog time-gated pulse counters and then read out by column-parallel single-slope (SS) analog-to-digital converters (ADCs). We present two prototypes of iToF sensors that exploit one- or two-tap counters in the pixel. Compared to the one-tap sensor, the two-tap sensor achieves an improved fill factor of 26.3% with a pixel pitch of 32 μm. This improvement is realized by using a retrograde deep n-well as guard-ring structure and two analog counters whose layout has been optimized. By utilizing two different demodulation frequencies of 1.56 and 50 MHz, the two-tap sensor achieves a large depth range of 50 m with a relative depth uncertainty of 0.22% and a high 3-D frame rate of 65 frames/s. When using an optical bandpass filter and multi-frame accumulation, the sensor shows a tolerance of 120-klx sunlight. Compared with the previous iToF benchmarks, the proposed SPAD-based iToF sensor demonstrates the largest depth range without compromising the relative depth uncertainty.

Original languageEnglish
Pages (from-to)2956-2967
Number of pages12
JournalIEEE Journal of Solid-State Circuits
Issue number10
Publication statusPublished - 2021 Oct

Bibliographical note

Funding Information:
Manuscript received January 17, 2021; revised April 15, 2021 and June 9, 2021; accepted June 23, 2021. Date of publication July 15, 2021; date of current version September 24, 2021. This article was approved by Associate Editor Jun Deguchi. This work was supported by the Korea Medical Device Development Fund Grant through the Korea Government (the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health and Welfare, and the Ministry of Food and Drug Safety) under Project KMDF_PR_20200901_0048 and Project 1711138024. (Corresponding author: Youngcheol Chae.) Byungchoul Park, Chanmin Park, Woojun Choi, Yoondeok Na, and Youngcheol Chae are with the Department of Electrical and Electronic Engineering, Yonsei University, Seoul 03722, South Korea (e-mail: ychae@yonsei.ac.kr).

Publisher Copyright:
© 1966-2012 IEEE.

All Science Journal Classification (ASJC) codes

  • Electrical and Electronic Engineering


Dive into the research topics of 'A 64 × 64 SPAD-Based Indirect Time-of-Flight Image Sensor with 2-Tap Analog Pulse Counters'. Together they form a unique fingerprint.

Cite this