To measure the distance to points on an object by radiating a periodic amplitude-modulated optical signal to the object and detecting the phase difference between the radiated optical signal and a reflected optical signal from the object, a first photo-detection control signal is generated to control the radiation of the optical signal. A mask signal is generated such that the mask signal is activated at least during a shuttering duration for resetting the voltage level at a sensing node (associated with an operation of a previous frame). A second photo-detection control signal is generated based on the first photo-detection signal and the mask signal such that the second photo-detection signal is deactivated or masked at least during the shuttering duration.