Focal-plane on-line nonuniformity correction using floating-gate adaptation

We develop stochastic adaptive algorithms for on-line correction of spatial nonuniformity in random-access addressable imaging systems. The adaptive architecture is implemented in analog VLSI, integrated with the sensors on the focal plane. Random sequences of address locations selected with predetermined statistics are used to adaptively equalize the intensity distribution at a variable spatial scale. Through a logarithm transformation of system variables, adaptive gain correction is achieved through offset correction in the log-domain. This idea is particularly attractive for compact implementation using translinear floating-gate MOS circuits. The technique applies to a variety of solid-state imagers, such as artificial retinas and IR sensor arrays. Experimental results confirm gain correction in a 64×64 pixel adaptive array integrated on a 2.2 mm×2.25 mm chip in 1.2 μm CMOS technology