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The response time of a comparator in a time-pickoff circuit used for time measurement depends on the slope and the overdrive of its input signal. Thus, the generation time of the timing pulse in a time-pickoff circuit is dependent on the amplitude of the input signal, which is the main cause of a timing error. In this study, a time-pickoff method, which employs an automatic gain control (AGC) circuit, is proposed for reducing the timing error called time walk. The AGC circuit in front of the comparator renders the amplitude of the input signals to the comparator to be uniform and the proposed method can be arranged to be relatively independent of the properties of the comparator. The performance of the proposed time-pickoff method was tested and its effectiveness was confirmed through the experiments. It is found that the time walk of the proposed time-pickoff method is less than 227 ps for input signals with a rise time less than 1 ns and a dynamic range of 40 dB.