According to at least some example embodiments of the inventive concepts, a sensor includes a pixel array including a pixel configured to generate a first pixel signal and a second pixel signal, based on a light sensed during a window time of a sensing time; processing circuitry configured to select a measuring range from among a plurality of measuring ranges and set a width of the window time based on the selected measuring range; a converting circuit configured to convert the first and second pixel signals into digital signals; and a driving circuit configured to generate an overflow control signal, a first photo gate signal, and a second photo gate signal so as to sense the light during the window time, wherein the pixel includes, a photoelectric conversion element, first and second readout circuits configured to receive charges, and an overflow transistor configured to remove charges.