Analog-to-digital converting circuit for optimizing power consumption of dual conversion gain operation, operation method thereof, and image sensor including the same

An image sensor comprising:

• a pixel array configured to output a first pixel signal corresponding to a first conversion gain from a first pixel and output a second pixel signal corresponding to a second conversion gain from the first pixel;
• and
• an analog-to-digital converting circuit configured to output a first digital signal corresponding to the first pixel signal,
• wherein the analog-to-digital converting circuit is configured to output a second digital signal corresponding to the second pixel signal based on a value of a most significant bit (MSB) of the first digital signal,
• wherein the first conversion gain is higher than the second conversion gain,
• wherein the pixel array comprises a floating diffusion region connected to the first pixel and a plurality of pixels connected to the floating diffusion region,
• wherein the floating diffusion region has a first capacitance value when the pixel array outputs the first pixel signal,
• wherein the floating diffusion region has a second capacitance value greater than the first capacitance value when the pixel array outputs the second pixel signal, and
• wherein the analog-to-digital converting circuit is configured to output the second digital signal based on a comparison result between the value of an MSB of the first digital signal and a threshold value.