Design of a self-correcting active pixel sensor

Abstract

Digital cameras are growing ever larger in silicon area and pixel count, which increases the occurrence of defects at fabrication time, or dead pixels that develop over their lifetime. An active pixel sensor self-correcting for most common faults is created by splitting the photodiode and readout transistors into two parallel portions with only a small area cost. Simulations show operation is the same for a single large device with no faults. When one half of the redundant pixel is stuck at low, output over a wide current range is reduced by 1.98 to 2.01. For one half stuck at high, faults output, after offset removal, is reduced by a factor of 1.85 to 1.92. Hence self-correction of the pixel can be performed with good accuracy via a simple shift circuit and with high accuracy with digital processing. Variation in transistor threshold voltages between the pixel halves of even 10% only causes modification of factors by 2-4%, hence giving a small effect.