A 640 \times 640 Fully Dynamic CMOS Image Sensor for Always-On Operation

• Published in: IEEE journal of solid-state circuits Vol. 55; no. 4; pp. 898 - 907
• Main Authors: Park, Injun, Jo, Woojin, Park, Chanmin, Park, Byungchoul, Cheon, Jimin, Chae, Youngcheol
• Format: Journal Article
• Language: English
• Published: IEEE 01.04.2020
• Subjects: Always-on; Analog-digital conversion; Capacitors; CMOS image sensor; CMOS image sensors; dynamic bias comparator; dynamic single-slope (SS) analog-to-digital converter (ADC); dynamic source follower (SF); Energy resolution; fully dynamic CMOS image sensor; Image resolution; Power demand; two-step counter
• ISSN: 0018-9200; 1558-173X
• DOI: 10.1109/JSSC.2019.2959486

This article presents a 640 <inline-formula> <tex-math notation="LaTeX">\times </tex-math></inline-formula> 640 fully dynamic CMOS image sensor for the always-on operation. It consists of a dynamic pixel source follower (SF), whose output signal is sampled into a parasitic column capacitor and then read out by a dynamic single-slope (SS) analog-to-digital converter (ADC) based on a dynamic bias comparator and an energy-efficient two-step counter. The prototype sensor was implemented in a 110-nm CMOS process, achieving 0.3% peak non-linearity, 6.1 e − rms random noise (RN), and 67-dB dynamic range. The power consumption is only 2.1 mW at 44 frames per second (fps) and is further reduced to 140 <inline-formula> <tex-math notation="LaTeX">\mu \text{W} </tex-math></inline-formula> at 5 fps with the sub-sampled 320 <inline-formula> <tex-math notation="LaTeX">\times </tex-math></inline-formula> 320 mode. This sensor achieves a state-of-the-art energy efficiency figure-of-merit of 0.71 e − <inline-formula> <tex-math notation="LaTeX">\cdot </tex-math></inline-formula>nJ.