Patent ID: 8508629

Claim:
An image sensor, comprising: an image pixel array to generate analog image signals in response to incident light; a dark pixel array to generate analog black reference signals for analog black level calibration of the analog image signals; a data bit line coupled to a line of image pixels within the image pixel array for transferring out the analog image signals from the line of image pixels; a plurality of reference bit lines coupled to a corresponding plurality of lines of black reference pixels within the dark pixel array for transferring out the analog black reference signals from the lines of black reference pixels; a driver coupled to the reference bit lines to receive the analog black reference signals; a comparator coupled to receive the analog image signals from the data bit line and coupled to receive the analog black reference signals output from the driver, the comparator coupled to offset the analog image signals with the analog black reference signals in an analog domain; and an analog-to-digital converter (“ADC”) circuit coupled to an output of the comparator, wherein the driver comprises a unit gain buffer including: a non-inverting input coupled to the reference bit lines; an inverting input; and a feedback path coupling an output of the unit gain buffer to the inverting input.