Method and apparatus to extend dynamic range of time delay and integrate charge coupled devices

Abstract

A novel method and apparatus is disclosed that is able to extend the intra-scene dynamic range of Time Delay and Integrate Charge-Coupled Device imagers. In accordance with the principles of the invention, the charge collected and accumulated over a plurality of photosensitive devices is limited by adjusting the barrier levels at which collected accumulated charge is removed from the photosensitive devices. By limiting the amount of accumulated charge that is collected, images of high intensity are prevented from overflowing or saturating the photosensitive devices. Thus, information that is included in the brighter levels of the image is not lost because of clipping the photosensitive device to prevent saturation. In one embodiment of the invention, the blooming barrier levels are adjusted in a step-wise linear manner to allow a known amount of charge to be retained during the initial collection phase while allowing progressively greater amounts of charge to be retained as the collection phase proceeds. This stepped increase in barrier level causes the imager to compress highly intense images to prevent saturation during the initial collection phase, while not influencing the response to images of lower intensity.