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

This article presents a 640 × 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 μW at 5 fps with the subsampled 320 × 320 mode. This sensor achieves a state-of-the-art energy efficiency figure-of-merit of 0.71 e ^- ·nJ.