Image sensor

An image sensor comprising:

• a first capacitor and a second capacitor arranged between an input terminal and a first node;
• a first comparing unit having a positive input terminal connecting to a first reference signal, a negative input terminal connecting to a connecting node of the first capacitor and the second capacitor, and an output terminal connecting to the first node wherein the first comparing unit provides a first preliminary ramp signal or a second preliminary ramp signal on the first node;
• a first switch and a second switch arranged between the input terminal and the first capacitor to selectively connect the first capacitor to a ground voltage or the input terminal;
• a third capacitor connecting to the second capacitor in parallel;
• a third switch selectively connecting the first node to the third capacitor;
• a first ramp signal output unit generating a first ramp signal by using the first preliminary ramp signal when the first preliminary ramp signal is provided;
• and
• a second ramp signal output unit generating a second ramp signal by using the second preliminary ramp signal when the second preliminary ramp signal is provided.