Linear calibration system and method for time-to-digital converter and digital phase-locked loop

The present disclosure provides a linear calibration system for a time-to-digital converter and a method thereof, and a digital phase-locked loop. The linear calibration system includes a digitally controlled reference delay circuit for receiving a first clock signal and delaying the first clock signal to generate a reference clock signal, a time-to-digital conversion circuit including at least two time-to-digital converters, and a state machine. The time-to-digital conversion circuit receives the first clock signal and the reference clock signal, delays the first clock signal to generate a first delay signal, compares a phase of the first delay signal with a phase of the reference clock signal, and outputs a phase detection result signal. The state machine generates a delay control signal for controlling the digitally controlled reference delay circuit, adjusts a calibration control signal to align the phases of the first delay signal and the reference clock signal.