Signal and noise modeling and analysis of complementary metal-oxide semiconductor active pixel sensors

The active pixel sensor (APS) structure is the most common pixel element for photodetection systems in standard complementary metal-oxide semiconductor technology. The focus of our work is on finding functional characteristics for low-light level design. Shot, reset, thermal, and $1∕f$ noise sources are considered in APS noise modeling. We also consider a higher-order empirical model for the $p-n$ junction capacitance to accurately calculate the signal value. Signal-to-noise ratio curves are then determined for various values of integration time, signal level, and other design parameters. These curves can lead to the optimum operating point of the APS element.