A pixel circuit for a depth sensor operating in a detection period and an output period in either a first operating mode (high incident light intensity) or a second operating mode (low incident light intensity). The pixel circuit includes a light receiving unit generating charge in response to the incident light, a signal generation unit accumulating charge in a FDN in response to a transmission signal, reset signal and selection signal during the detection period, and generating an analog signal having a level corresponding to a voltage apparent at the FDN during the output period, and a refresh transistor coupled between a supply voltage and the light receiving unit and discharging charge to the supply voltage in response to a refresh signal.