Abstract

Disclosed is an image sensor having A/D conversion circuitry coupled to column data lines of an image sensor array. The A/D conversion circuitry digitizes analog signals on the column data lines, each representing intensity of light incident upon an active imager cell. Higher resolution is provided for darker light levels than for bright light levels, such that a high resolution image is obtained with less storage data than would otherwise be required. In one embodiment, the A/D conversion circuitry includes a plurality of comparators, each having a first input coupled to one or more column data lines and a second input coupled to receive a time-varying reference signal, and a plurality of n-bit counters coupled to the comparator outputs. An n-bit to m-bit converter nonlinearly maps n-bit codes to m-bit codes and provides the m-bit codes to an m-bit D/A converter which produces the time-varying reference signal. In another embodiment, the A/D conversion circuitry is comprised of a non-uniform successive approximation A/D converter.