Analog-to-digital converting circuit using auto-zero period optimization and operation method thereof

An operation method of an analog-to-digital converting circuit including a first amplifier and a second amplifier, the method comprising:

• equalizing voltage levels of input nodes and an output node of the first amplifier in response to a first auto-zero signal in a first auto-zero period;
• charging a capacitor of the second amplifier in response to a second auto-zero signal in a second auto-zero period;
• stopping an operation of the second amplifier from a time point at which the second auto-zero period ends to a time point at which a first operation period starts;
• generating a first output signal by comparing a ramp signal and a reset signal of a pixel signal output from a pixel array during the first operation period and comparing the ramp signal and an image signal of the pixel signal during a second operation period after the first operation period;
• and
• generating a second output signal based on the first output signal in the first and second operation periods.

A circuit which charges a capacitor in response to an auto-zero signal in an auto-zero period and generates an output signal in an operation period, the circuit comprising:

• a first transistor configured to provide a power supply voltage to a first output node from which the output signal is output;
• a second transistor connected to the capacitor through a bias node, and configured to turn on in response to the auto-zero signal;
• a current source connected to the first transistor through the first output node, connected to the capacitor and the second transistor through the bias node, and configured to generate a power current based on a voltage level of the bias node, which is maintained by the capacitor;
• and
• a third transistor connected to the first transistor, and configured to provide the power supply voltage to the first transistor and turn off in response to a power down signal such that an operation of the circuit is stopped.