Patent ID: 7864229

Claim:
An analog to digital converting device, comprising: a first correlated double sampling (CDS) circuit configured to generate a first sampling signal by performing CDS on an active pixel output signal output from an active pixel and to generate a first comparison signal by comparing the first sampling signal with a reference signal, the first CDS circuit being configured to generate the first sampling signal in response to a ramp signal and the active pixel output signal; a second CDS circuit configured to generate a second sampling signal by performing CDS on an OB pixel output signal output from an optical black (OB) pixel and to generate a second comparison signal by comparing the second sampling signal with the reference signal, the second CDS circuit being configured to generate the second sampling signal in response to a DC signal and the OB pixel output signal; and a reference signal generator configured to output the second sampling signal or a signal related to the DC signal as the reference signal in response to a switching signal, wherein the reference signal generator includes: a first buffering circuit configured to generate a mid signal by buffering an input analog signal; a second buffering circuit configured to generate the DC signal by buffering the mid signal; a switch configured to output an output signal of the first buffering circuit or one of the second sampling and second comparison signals in response to the switching signal; and a third buffering circuit configured to generate the reference signal by buffering an output signal of the switch.