A time-to-digital converter (TDC) comprises a TDC core and a masking circuit. The TDC core is configured to detect phase difference between a reference signal and a controlled signal. The masking circuit is configured to generate a mask signal based on the reference signal, the controlled signal, and a command signal including information of a predetermined value associated with the reference signal and the controlled signal. The mask signal is used to mask a portion of pulses of the controlled signal from entering the TDC core during detection of phase difference.