Image sensing device using a single analog to digital conversion operation on pixal signals and operating method thereof

An image sensing device comprising:

• a first sampling circuit suitable for sampling a first reference ramp signal as a first ramp signal;
• a second sampling circuit suitable for sampling a second reference ramp signal as a second ramp signal;
• a first switching circuit suitable for outputting first and second pixel signals to a first common node according to a first order based on first and second control signals;
• a third sampling circuit suitable for sampling the first and second pixel signals, which are outputted through the first common node, as a first measurement signal;
• a second switching circuit suitable for outputting the first and second pixel signals to a second common node according to a second order, which is opposite to the first order, based on third and fourth control signals;
• and
• a fourth sampling circuit suitable for sampling the first and second pixel signals, which are outputted through the second common node, as a second measurement signal;
• a comparison circuit suitable for simultaneously comparing the first and second ramp signals with the first and second measurement signals and generating a comparison signal corresponding to a comparison result.