A readout integrated circuit configured to read out sensing signals from an optical sensing panel including a sensor array for fingerprint sensing is provided. The readout integrated circuit includes a plurality of input terminals, a comparator circuit and a control circuit. The plurality of input terminals are configured to be coupled to a plurality of output terminals of the optical sensing panel. The comparator circuit is configured to receive an output voltage from an output terminal of the plurality of output terminals of the optical sensing panel and at least one reference voltage, compare the output voltage to the at least one reference voltage and output a comparison result. The control circuit is coupled to the comparator circuit. The control circuit is configured to receive the comparison result and determine a supplementary charge amount to be charged to or discharged from the output terminal according to the comparison result.