CMOS image sensor readout employing in-pixel transistor current sensing

We propose an analog CMOS image sensor with 10X faster readout settling time than standard active pixel sensor (APS) designs. The pixel in the proposed design is a standard APS source follower configuration thus retaining high fill factor. Negative feedback is applied to the readout of the pixel from a column shared circuit to increase its current driving capabilities and thereby reduce the settling time between correlated double sampling (CDS) samples, which significantly reduces the 1/f noise contributed by the in-pixel source follower transistor. In addition, we describe an improved active reset utilizing the current sensing method. We present analysis and simulations of the proposed current sensing active pixel (CSAP) sensor design in a standard 0.35 um CMOS process operating from a 3.3 V power supply.