Patent ID: 8149022

Claim:
A frequency synthesizer comprising: a delta-sigma modulator for receiving a period control word and generating a phase selection signal; and a delay line unit for generating an output clock and a second control signal based on the phase selection signal and a second clock, the delay line unit comprising: a digital delay line for receiving the second clock and generating the output clock according to the phase selection signal; a delay unit for receiving the second clock and generating a delayed second clock; a dummy delay line for receiving the delayed second clock and generating a third clock; and a phase detection unit for receiving the output clock and the third clock, and generating the second control signal according to a phase relationship between the output clock and the third clock; wherein the delta-sigma modulator performs a carry-in operation based on a base number and the base number is adjustable and determined by a calibration process of the delay line unit, and the delta-sigma modulator comprises: an adder for generating a difference signal by adding the period control word with a first control signal; and a value setting device for generating the first control signal; wherein the delta-sigma modulator generates a carry signal according to the difference signal, and the value setting device receives the carry signal and the second control signal, and provides the first control signal to the adder for performing the carry-in operation.