A frequency synthesizer includes an oscillator for providing an RF clock, a phase shifter arranged to provide a shifted reference clock by changing phase of a frequency reference clock, and a time-to-digital converter (TDC) for producing a digital TDC output by quantizing a time difference between said RF clock and said shifted reference clock; wherein a range of said TDC covers significantly less than a full range of said RF clock period. An associated method is also provided.