This paper presents a 100 kS/s, 1.3 μW, 9.3 ENOB successive approximation ADC with a time-domain comparator. The proposed time-domain comparator utilizes a differential multi-stage VCDL, resulting in a highly digital operation eliminating static power consumption. The effects of gain, noise, and offset are also investigated by detailed analysis which proves the feature of reducing the input-referred noise and offset by simply increasing the number of delay stages. For verification, the proposed ADC is fabricated in a 0.18 μm CMOS. With a single supply voltage of 0.6 V, the ADC consumes 1.3 μW at the maximum sampling rate of 100 kS/s. The measured ENOB is 9.3 b showing a figure of merit of 21 f J/conversion-step.