Design issues on CMOS space-variant image sensors

A new image sensor, using CMOS technology, has been designed and fabricated. The pixel distribution of this sensor follows a log-polar mapping, thus the pixel concentration is maximum at the center reducing the number of pixels toward the periphery, having a resolution of 56 rings with 128 pixels per ring. The design of this kind of sensors has special issues regarding the space-variant nature of the pixel distribution. The main topic is the different pixel size that requires scaling mechanisms to achieve the same output independently of the pixel size. This paper present some study results on the scaling mechanisms of this kind of sensors. A mechanism for current scaling is presented. This mechanism has been studied along with the logarithmic response of these special kind of sensing cells. The chip has been fabricated using standard 0.7 mu m CMOS technology.