The present disclosure relates to a digital subsampling phase-locked-loop (PLL) with a digital-to-time converter (DTC) based successive-approximation-register (SAR) phase estimation. This disclosed PLL utilizes a DTC and a one-bit sampler to generate one phase word by calculating multiple one-bit phase measurements with a SAR algorithm. The one phase word, which indicates the phase estimation of a radio frequency (RF) output signal compared to a reference signal, enables the PLL to lock the RF output signal with the reference signal in a short settling time. In addition, utilizing the one-bit sampler instead of a conventional frequency divider is good for linearity and low power consumption of the PLL without introducing significant noise in the RF output signal.