Self-scanned image sensors based upon bucket-brigade scanning

Image sensors employing the charge-transfer principles of the bucket-brigade delay line for internal scanning offer potential advantages over the usual x-y addressed sensors in simplicity of fabrication. A design for a self-scanned bucket-brigade sensor that can be fabricated upon a monolithic silicon wafer with a single diffusion and one layer of metallization is proposed. An experimental array has been built comprising 15 rows of 32 series-connected MOS transistors whose sources and drains serve as photodiodes. These transistors are interconnected to adjacent horizontal buses so that each row can function independently as a shift register. In operation, each register remains inactive for a period of time during which an image charge pattern is built up on the photodiodes. The application of the horizontal clock pulses to that row causes the charge pattern to be transferred stepwise to the edge of the array where it is converted into a video signal. Although in the test sample the gating of the horizontal clock pulses to successive rows was accomplished by means of an external vertical scan generator, this could be replaced by an integrated vertical register formed on the same chip with the sensor.