A readout integrated circuit configured to read out sensing signals from an optical sensing panel is provided. The optical sensing panel includes a sensor array for fingerprint sensing. The readout integrated circuit includes a plurality of input terminals and a first discharging circuit. The plurality of input terminals are coupled to a plurality of output terminals of the optical sensing panel. The first discharging circuit is coupled to one of the plurality of input terminals. The first discharging circuit serves to discharge an output terminal included in the plurality of output terminals of the optical sensing panel by a first current during a readout period. The readout integrated circuit reads out a voltage of the output terminal as a sensing signal. The first discharging circuit includes a first switch element controlled by a control signal and a first current source which generates the first current.