CMOS foveated image sensor: signal scaling and small geometry effects

A new foveated (log-polar) image sensor using standard CMOS technology has been designed and fabricated. The pixel distribution follows the log polar transform having more resolution in the center than in the periphery. For the fovea or central part, a different but also polar distribution has been adopted to fit the inner pixels. The particular problem of foveated image sensors is the signal scaling; pixels at different positions are different sizes and therefore different signal responses to the same illumination level. The difference among pixel responses is not only due to the differences among sensitive areas, but also to the differences among transistor channel sizes that, for submicron technologies, become a nonlinear problem. Some solutions for the signal scaling, small geometry effects (especially narrow-channel effects), and foveated structure, have been analyzed and successfully adopted for the presented sensor. The election of the CMOS process, instead of the CCD, is also discussed and analyzed.