A compact time-to-amplitude converter (TAC) for single-photon time-of-flight (TOF) measurement was designed. An innovative current integral method based on Wilson current source was proposed to effectively reduce the circuit occupied area and to significantly enhance the time full-scale range (FSR) of the TOF measurement. Designed in a standard 018 μm CMOS technology, the filling factor (FF) of 268% was achieved through a compact TAC structure for a single-photon avalanche diode (SPAD) pixel. The post-layout simulation results further revealed that the TAC featured 230 ps timing resolution in a 120 ns FSR. Furthermore, the TAC was characterized by a low differential nonlinearity (DNL) of 005 LSB and a low integral nonlinearity (INL) of 11 LSB in the whole detectable time range. Additionally, a low nonuniformity below 05 % was obtained across 512 in-pixel TACs by Monte Carlo simulation. The proposed TAC was very suitable for high-density time-correlated single-photon counting (TCSPC) detectors.