Analog-to-digital converting circuit for optimizing dual conversion gain operation and operation method thereof

A circuit, comprising:

• a first transistor configured to receive a first pixel signal corresponding to a first conversion gain and a second pixel signal corresponding to a second conversion gain;
• a second transistor configured to receive a first ramp signal and a second ramp signal;
• a first current source connected with a first source terminal of the first transistor and a second source terminal of the second transistor at a common node, and configured to output a first sub power current;
• a switch connected with the first source terminal and the second source terminal at the common node;
• and
• a second current source connected with the switch, and configured to output a second sub power current,
• wherein the first conversion gain is higher than the second conversion gain,
• wherein a first power current of the circuit when the first pixel signal and the first ramp signal are compared is different from a second power current of the circuit when the second pixel signal and the second ramp signal are compared.