Frequency synthesizer and associated method

A frequency synthesizer comprising:

• an oscillator for providing a variable clock;
• a phase shifter coupled to said oscillator, and arranged to provide a shifted variable clock whose phase is arranged to be different from phase of said variable clock by a phase offset, wherein said phase offset is such arranged that a time difference between a transition of a frequency reference clock and a prior transition of said shifted variable clock is less than a period of said variable clock;
• and
• a time-to-digital converter (TDC) coupled to said phase shifter, and arranged to provide a first fractional error correction signal by quantizing said time difference.

A frequency synthesizer comprising:

• an oscillator for providing a variable clock;
• a time-to-digital converter (TDC) arranged to provide a first fractional error correction signal by quantizing a time difference between a frequency reference clock and a shifted variable clock, wherein phase of said shifted variable clock is arranged to be different from phase of said variable clock by a phase offset;
• and
• a shift controller arranged to provide a second fractional error correction signal in response to an accumulated value of a frequency command word (FCW);
• wherein said oscillator is further arranged to tune periods of said variable clock according to said first fractional error correction signal and said second fractional error correction signal.

A method of synthesizing a frequency by providing a variable clock, comprising:

• generating said variable clock in response to an oscillator tuning signal;
• phase shifting said variable clock by a phase offset to obtain a shifted variable clock;
• and
• digitizing a timing difference of said shifted variable clock and a frequency reference clock such that a range of said digitizing covers less than a full range of said variable clock period.