A vision sensor with on-pixel ADC and in-built light adaptation mechanism

In this paper we propose an on-pixel Analogue-to-Digital Converter (ADC) based on pulse frequency modulation (PFM) scheme. This PFM based converter presents a viable solution for pixel-level based ADC. It uses a simple and robust circuit that can be implemented in a compact area resulting in a 23% fill-factor for a digital vision sensor in 0.25 mum CMOS technology. An in-built light adaptation mechanism has also been implemented which allows the sensor to better adapt to low-light intensity or to adjust the sensor saturation level. As a consequence, the proposed sensor features a programmable dynamic range. Image lag is eliminated since a reset of the photodetector is performed after the conversion period. A prototype comprising a 32 X 32 pixel array has been implemented in CMOS 0.25 mum technology. Each pixel occupies an area of 45 X 45 mum(2) with an average power consumption of 85 LW per pixel. (C) 2002 Elsevier Science Ltd. All rights reserved.