Object location and centroiding techniques with CMOS active pixel sensors

A system based on a pixel-parallel CMOS active pixel sensor architecture is demonstrated for capturing the location and approximate size of an object. The object is distinguished from the background by a global threshold. Three prototype sensors are implemented in standard CMOS technologies. In the first, a high fill factor three-transistor pixel with integral comparator is demonstrated. It is shown that performance of this sensor is limited by device nonuniformities, so a novel in-pixel fixed-pattern noise correction circuit using a single capacitor is demonstrated in the second sensor. The system concept is further enhanced by a cumulative cross section readout architecture which provides additional information regarding the object with little reduction in speed. The application of these systems to centroid determination using multiple thresholds is discussed.