Photodiode-Based CMOS APSs With Zero-Lag, Low-Noise, High-Linearity Design

Two improved schemes for the design and operation of photodiode-based CMOS (complementary metal oxide/ semiconductor) active-pixel sensors (APSs) afford zero image lag, low noise, and high linearity of response even under low illumination. Figure 1 schematically depicts the circuitry for one pixel according to a typical older scheme. In soft reset, the sensing node does not charge up to the power-supply potential (VDD), and depends strongly on the potential at the beginning of the reset. In hard reset, the sensing node charges up to a known potential, usually VDD.