Fixed-Pattern-Noise Correction for an Integrating Wide-Dynamic-Range CMOS Image Sensor

A 100 × 98 CMOS image sensor (CIS) fabricated in a standard 0.35-μm CMOS technology is described. The pixels in this CIS integrate the photocurrent in each pixel for a time that depends upon the photocurrent to map wide-dynamic-range (WDR) real-world scenes to a lower DR output. To improve their low-light sensitivity, these pixels include a MOSFET that restricts the voltage changes on the photodiode. In addition, the user-defined input voltage needed to generate a WDR response is one that preserves the low-light sensitivity of the pixels. This results in pixels with a linear response at low photocurrents and a logarithmic response at larger photocurrents. Results are presented, which show that a fixed-pattern-noise (FPN) correction procedure based upon assuming either a linear or a logarithmic response introduces artifacts into some images. An FPN correction procedure that both avoids these artifacts and accurately estimates the mean photocurrent in the array is then presented.