Comparator with correlated double sampling scheme and operating method thereof

A comparator comprising:

• a comparison block suitable for comparing a pixel signal and ramp signals having different slopes for respective steps;
• a CDS block suitable for performing CDS, the CDS block being coupled between a fourth input terminal receiving the pixel signal and a negative input terminal of the comparison block, and suitable for performing CDS;
• a first switch installed between the CDS block and a first input terminal receiving a first ramp signal used for first and second steps;
• a first capacitor coupled between a ground terminal and the CDS block;
• a second switch coupled between a second input terminal receiving a second ramp signal used for a third step and a positive input terminal of the comparison block;
• a second capacitor installed between a third input terminal receiving a third ramp signal for a fourth step and the positive input terminal of the comparison block;
• an amplification block suitable for buffering a comparison signal outputted from the comparison block;
• and
• a feedback control unit suitable for generating first and second switch control signals for controlling the first and second switches based on the buffered comparison signal,
• wherein the first ramp signal is retained as a constant value during the second step, and changed to have a slope different from a slope of the first step during the third step.

An operating method of a comparator with CDS scheme, the operating method comprising:

• performing a rest operation;
• performing a first step operation;
• performing a second step operation;
• and
• performing a third step operation,
• wherein the performing of the first step operation comprises re-inputting a pixel signal and storing a difference value between the re-inputted pixel signal and a first ramp signal, when a logic level of a comparison signal is changed during the first step operation, and
• wherein the first ramp signal is retained as a constant value during the second step operation, and changed to have a slope different from a slope of the first step during the third step operation.