A CMOS vision sensor with on-the-fly histogram equalization using TFS encoding and AER read-out

This paper presents a CMOS vision sensor performing image capture and on-chip histogram equalization. Both image capture and the processing are based on time-to-first spike encoding combined with address event representation (AER) read-out scheme. The proposed approach not only provides a compact and efficient VLSI implementation but also eliminates voltage/current domain analog processing and hence provides immunity to dynamic range reduction caused by low voltage operation in advanced sub-micron technologies. The pixel values are read-out using an asynchronous handshaking type of read-out while the processing is carried out using simple and yet robust digital timer occupying a very small silicon area (0.1 times 0.6mm² in 0.35mum CMOS). Low power operation (10nA per pixel) is achieved since the pixels are only allowed to switch once per frame and only active pixels are allowed to asynchronously access the bus. The prototype was implemented in 0.35mum CMOS technology with a silicon area of 3.1 times 3.2mm²