CMOS image sensor with logarithmic response and self-calibrating fixed pattern noise correction

Abstract

Optical CMOS sensor arrays have to cope with the problem of mismatch between individual pixels. This paper describes a CMOS camera chip with logarithmic response that has an automatic analog fixed pattern noise correction on chip. It was fabricated in an 0.8 micron process and consists of 64 X 64 active pixels. The photoreceptors show a measured response of about 100 mV per decade in light intensity and a dynamic range of more than 6 decades. Each pixel includes a capacitor to store the offset correction voltage. After applying the calibration procedure the remaining fixed pattern noise of one column has a standard deviation of 2 mV corresponding to 2 percent of a decade. The result is a system with significantly reduced pixel to pixel variations in comparison to similar uncalibrated photoreceptor arrays.