An image sensor includes a photo gate controller configured to generate a plurality of demodulated signals respectively corresponding to a plurality of rows of a pixel array and a photo gate driver configured to adjust a phase of the demodulated signals using a source clock signal to remove power, voltage and temperature (PVT) noise and to apply the phase-adjusted demodulated signals to the pixel array. The image sensor matches the phases of the respective demodulated signals using the source clock signal generated based on a reference clock signal, thereby increasing the quality of depth images.