This paper presents an all-digital on-chip supply voltage sensor that captures one-shot voltage fluctuation every clock cycle. The proposed sensor was implemented on ASIC in 65nm process and FPGA. The obtained voltage resolution was 3.9mV and 29mV, respectively. This sensor is suitable for providing voltage information to trace-based error localization system. We experimentally show that the proposed sensor contributes to the facilitation of error localization.