A 90nm CMOS multimode image sensor intended for a visual cortical stimulator

We present in this paper a variable resolution multimode digital pixel sensor (DPS). Each pixel comprises a switched-capacitor comparator with a regenerative 8-bit memory. Two supply voltages, 2.5 V and IV, are used to maximize the dynamic range (DR) of the sensor. The proposed DPS has three modes of operation: linear with the option of multiple exposures, logarithmic for extended dynamic range, and high-speed differential mode for the subtraction of two consecutive images. Intended for the front-end of a visual cortical stimulator aiming at restoring sight to the blind, the proposed circuit, which encompasses a matrix of 64times48 pixels, allows acquiring images at a rate higher than 400 frames per second (fps). Implemented in a 90 nm CMOS technology, each pixel has an area of 9 mum times 9 mum and a fill factor of 26%. A DR of up to 83 dB is obtained when the DPS is operated in its logarithmic mode.