A 256/spl times/256 CMOS differential passive pixel imager with FPN reduction techniques

Passive pixel sensors provide an alternative to the conventional active pixel sensor (APS) for high-density CMOS imaging arrays. Similar to the history of the single-transistor DRAM cell, this one-transistor pixel cell has one main advantage over the APS. It has high fill-factor in a smaller area, leading to a high-density array of pixels with high quantum efficiency. Experiments reveal a major weakness in passive pixels is a signal-dependent parasitic current that can contaminate charge signals in different parts of the array. The origin of this parasitic current is explained here. A correlated double sampling (CDS) circuit in a differential architecture removes its effects.