Patent ID: 8179455

Claim:
An Optical Black Pixel (OBP) cancellation circuit comprising: a pixel input receiving a pixel pulse from an image sensor; an output indicating an average black-level signal; a differential amplifier having a first differential input and a second differential input and generating the output from a voltage difference between the first differential input and the second differential input; a feedback switch coupled between the output and the first differential input; a feedback capacitor coupled to the first differential input and a first feedback node; a series feedback switch coupled between the first feedback node and the output; an accumulating switch coupled between a reference node carrying a reference voltage and the second differential input; an accumulating capacitor coupled to the second differential input and a second accumulating node; a series accumulating switch coupled between the second accumulating node and the reference node; a first sampling capacitor coupled between the first differential input and a first sample node; a first secondary sampling switch coupled between a first sample input and the first sample node for connecting the first sample input and the first sample node during a secondary phase; a first primary sampling switch coupled between the output and the first sample node for connecting the output and the first sample node during a primary phase; a second sampling capacitor coupled between the second differential input and a second sample node; a second secondary sampling switch coupled between a second sample input and the second sample node for connecting the second sample input and the second sample node during the secondary phase; and a second primary sampling switch coupled between the pixel input and the second sample node for connecting the pixel input and the second sample node during the primary phase; wherein the pixel input is coupled to one of the first sample input and the second sample input; wherein the reference voltage is coupled to another one of the first sample input and the second sample input that is not connected to the pixel input.