Response properties of a foveated space-variant CMOS image sensor

A new foveated CMOS image sensor has been designed and fabricated. The photocell elements transform the light into current, and then, in a continuous way, into voltage without charge integration. This kind of sensing cell has been already employed in image sensors for normal cameras, but never in foveated sensors. The presented sensor tries to emulate the human eye pixel resulting in a sensor with a space variant distribution of pixels. Consequences of this distribution are the different size of the sensing elements in the pixel matrix, the non orthogonal shapes of the different elements that integrate the pixel, and, as a result, the different response of every cell in the sensor. A scaling mechanism is needed due to the different pixel size from circumference to circumference. A mechanism for current scaling is presented. This mechanism has been studied along with other effects, as the narrow channel effect on submicron MOS transistors, and the influence of the logarithmic response of these special kinds of sensing cells. The chip has been fabricated using standard 0.7 μm CMOS technology