Analysis of photoelectric conversion characteristics under knee control operation for CCD imagers

A high-light signal suppression operation, knee control operation, was evaluated in order to apply to a STACK-CCD of 2/3-in 2 M-pixel high definition television (HDTV) imager overlaid with an amorphous silicon photoconversion layer. A smooth bend was observed in the measured photoconversion characteristics near a knee point. It was analyzed theoretically by applying a subthreshold current of the MOSFET in weak inversion for skimming excess charges and reading out signal charges through a field shift gate. The calculated curve showed good agreement with the measured curve. Effectiveness of the knee control operation using the field shift gate was shown experimentally and theoretically over that using a conventional vertical overflow drain for IT-CCD imagers.<
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