CDS circuit, operating method thereof, and image sensor including CDS circuit

An image sensor comprising:

• a pixel configured to:
• output a first pixel signal in a first conversion gain mode;
• and
• output a second pixel signal in a second conversion gain mode;
• a ramp signal generator configured to generate a ramp signal of which a level falls with a slope;
• and
• a correlated double sampling (CDS) circuit configured to:
• receive the first pixel signal and the second pixel signal from the pixel through a column line;
• generate a first comparison result signal by comparing the ramp signal with the received first pixel signal;
• and
• generate a second comparison result signal by comparing the ramp signal with the received second pixel signal,
• wherein the CDS circuit comprises:
• a first comparator configured to:
• operate based on a first bias current;
• and
• compare, with the ramp signal, the received first pixel signal, during a first sub-period in a readout period for the pixel;
• and
• a second comparator configured to:
• operate based on a second bias current;
• and
• compare, with the ramp signal, the received second pixel signal, during a second sub-period in the readout period, the second sub-period being after the first sub-period, and
• wherein the first comparator is further configured to operate based on a third bias current that is lower than the first bias current, during the second sub-period, and
• wherein the second comparator is further configured to operate based on a fourth bias current that is lower than the second bias current, during the first sub-period.

An operating method of a correlated double sampling (CDS) circuit comprising a first comparator and a second comparator, the method comprising:

• generating a first reset value according to a first reset signal that is output from a pixel, by using the first comparator during a first period;
• generating a second reset value according to a second reset signal that is output from the pixel, by using the second comparator during a second period;
• generating a second image value according to a second image signal that is output from the pixel, by using the second comparator during a third period;
• and
• generating a first image value according to a first image signal that is output from the pixel, by using the first comparator during a fourth period, the second period being after the first period, the third period being after the second period, and the fourth period being after the third period,
• wherein, during the first period and the fourth period, the first comparator operates based on a first bias current, and
• wherein, during the second period and the third period, the first comparator operates based on a second bias current that is lower than the first bias current.