Suppression of edge effects arising in ccd imager field registers

Abstract

If drain structures bound the field register(s) of a CCD imager on the sides parallel to the direction of charge transfer therethrough, some portion of the charge carriers generated by photoemission will be lost to the drain structures from the charge transfer channels along those sides. If the charge transfer channels along those sides of the field register(s) do not have register boundary drain structures alongside them, on the other hand, charge carriers from the semiconductor substrate outside the field register(s) will migrate to them. These charge carriers may be thermally generated 'dark current', for example. In either case the side charge transfer channels do not have adjacent charge transfer channels that the other charge transfer channels in the field register(s) do, leading to undesired edge effects in the outputs of these side charge transfer channels. To eliminate the need for relatively complex blanking circuitry following the CCD output register, these outputs are not forwarded to the output register used for parallel-to-series conversion of image samples supplied from the field register(s).