Patent ID: 8144228

Claim:
An image sensor comprising: an active pixel sensor (APS) array configured to generate a reset signal and an image signal for a pixel of a selected column of the APS array; a calibration unit configured to generate a slope control signal for adjusting a ramp slope value; a ramp signal generator configured to generate a ramp signal based on the slope control signal, the ramp slope value of the ramp signal being adjusted based on the slope control signal; and an analog-to-digital converter (ADC) configured to generate a digital code based on the ramp signal and a difference between the reset signal and the image signal, the calibration unit including, an analog calibration unit configured to generate a first calibration code based on the ramp signal and a first threshold voltage and generate a second calibration code based on the ramp signal and a second threshold voltage; and a digital calibration unit configured to receive the first calibration code and the second calibration code from the analog calibration unit and generate the slope control signal based on the received first and second calibration codes.