Reliability and manufacturing costs due to defects is a significant problem with image sensors and the ability to recover from a fault would alleviate some of these costs. A fault-tolerant APS has been designed by splitting the APS pixel into two halves operating in parallel, where the photo sensing element has been divided in two and the readout transistors have been duplicated while maintaining a common row select transistor. This split design allows for a self correcting pixel scheme such

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... t if one half of the pixel is faulty, the other half can be used to recover the entire output signal. The fault tolerant APS design has been implemented in a 0.18µm CMOS process for both a photodiode based and photogate based APS. Test results show that the fault tolerant pixels behave as expected where a non-faulty pixel behaves normally, and a half faulty pixel, where one half is either stuck low or high, produces roughly half the sensitivity. The ratios of a normally operating pixel to a faulty pixel show an average value of 2.03 (stuck low) and 1.89 (stuck high) for the photodiode based APS, and 1.73 (stuck low) and 1.77 (stuck high) for the photogate based APS. Preliminary results indicate that the sensitivity of a redundant pixel is approximately three times that of a traditional pixel for the photodiode APS and approximately twice that for the photogate APS.