Time of flight sensing system and image sensor used therein

A time-of-flight (TOF) sensing system, comprising:

• an emitter configured to output a modulated signal having a preset phase;
• a receiver including an image sensor configured to receive a reflected signal which is reflected from a target;
• and
• signal processing circuitry configured to determine a distance from the target based on a phase relationship between the modulated light and the reflected light,
• wherein the image sensor comprises:
• a pixel array including plural pixels, each pixel including at least one photo diode and each pixel generating an amount of charge corresponding to the reflected light;
• comparing circuitry configured to compare voltage levels, each voltage level individually changed based on the amount of charge outputted from each pixel, with a reference voltage to output a comparison result;
• and
• calibration circuitry configured to adjust the voltage levels equally based on the comparison result.