Design of an APS CMOS image sensor for low light level applications using standard CMOS technology

CMOS image sensors (or APS: Active pixel sensors) are now the technology of choice for most imaging applications, such as digital video cameras. Where as their sensitivity doesn't reach the one of the best actual CCD's (whose fill factor is about 100%), they are now commonly used because of their mul tiple functionalities (windowing, on-chip signal processing) and their easy serial fabrication. In this paper, we present a study of different pixel p hotodiodes and architectures, in order to increase their sensitivity and re duce their spatial and temporal noise. These chips will be used in satellit e star trackers, and should be hardened to radiation. Two different architectures are investigated. The first one uses the photod iode capacitance for signal integration, as it is usually done in literatur e [1-3]. This capacitance should be as lower as possible, to increase conve rsion factor (the gain of the pixel) and reduce reset noise, and that's why different standard CMOS photodiodes have been studied and quantified. The second architecture uses a low-value poly1/poly2 capacitor inside each pixel for signal integration, thus resulting in increasing the gain but deg rading the fill factor.