Noise analysis of fault tolerant active pixel sensors

As digital imagers grow in pixel count and area, the ability to correct for pixel defects becomes more important. A fault tolerant active pixel sensor (APS) has previously been designed and fabricated that can correct for stuck high and stuck low defects. Analyses of the pixel noise for a standard APS and a fault tolerant APS are presented that consider reset noise, photocurrent shot noise, dark current shot noise, transistor thermal noise, transistor flicker noise, operational amplifier noise, and feedback resistor thermal noise. Under worst case conditions (no illumination), the noise of the fault tolerant APS is 1.106 /spl times/ more than a standard APS. At a typical illumination level, the fault tolerant APS noise is nearly unchanged to that of a standard APS. Previous research has shown that the fault tolerant APS is more sensitive than a standard APS, thus the overall signal-to-noise ratio of the fault tolerant APS should be greater than the standard APS except under very low light conditions.