Cmos analog front end architecture with variable gain for digital cameras and camcorders

Abstract

An image processing apparatus for charge coupled device (CCD) and video inputs in a digital camera or for a digital camcorder is disclosed which provides optical black and offset correction for CCD inputs. A sampling circuit, including correlated double sampler (CDS) ( ) and programmable gain amplifier ( ), samples the image input signal and the video input signal. CDS ( ) includes a single-ended amplifier ( ) and a differential amplifier ( ). The single-ended amplifier ( ) functions such that it is only operable during an CCD signal input; otherwise, the single-ended amplifier ( ) is bypassed such that a video signal is only sampled by the differential amplifier ( ). For CCD signals, the single-ended amplifier ( ) samples the reference level of the pixel and holds it during the video interval. The differential amplifier ( ) samples both the output of the single ended amplifier ( ) and the video level of the same pixel. Overall, the CDS ( ) subtracts these levels and converts the difference to a differential output to improve signal to noise performance and dynamic range. An analog-to-digital converter ( ) converts the sampled signal and feeds this digital sample to a digital correction circuit ( ) where optical black level, hot and cold pixels, and line noise are removed.