High Fill Factor Low-Voltage CMOS Image Sensor Based on Time-to-Threshold PWM VLSI Architecture

This paper presents a CMOS image sensor (CIS) VLSI architecture based on a single-inverter time-to-threshold pulsewidth modulation circuitry capable of operating as low as 330-mV supply voltage while retaining a signal-to-noise ratio of 24 dB; an important characteristic being demanded by very low voltage portable CIS-based equipment such as disposable medical cameras and on-chip autonomous wireless security vision systems. A 64 × 64 pixel array was fabricated using standard 130-nm CMOS process consuming only 5.9 nW/pixel with integration time of 2 ms at +0.5 V supply. The high fill factor of 58% facilitated a better SNR at a low supply voltage when compared with other CIS architectures. The pixel has a dynamic range of 54 dB with 7.8 frame per second.