Linear Current-Mode Active Pixel Sensor

A current mode CMOS active pixel sensor (APS) providing linear light-to-current conversion with inherently low fixed pattern noise (FPN) is presented. The pixel features adjustable-gain current output using a pMOS readout transistor in the linear region of operation. This paper discusses the pixel's design and operation, and presents an analysis of the pixel's temporal noise and FPN. Results for zero and first-order pixel mismatch are presented. The pixel was implemented in a both a 3.3 V 0.35 and a 1.8V 0.18 CMOS process. The 0.35 process pixel had an uncorrected FPN of 1.4%/0.7% with/without column readout mismatch. The 0.18 process pixel had 0.4% FPN after delta-reset sampling (DRS). The pixel size in both processes was 10times10 mum
²
, with fill factors of 26% and 66%, respectively.