Phase-locked loop frequency synthesizer and loop locking method thereof

Abstract

A phase-locked loop frequency synthesizer and a loop locking method thereof are provided. The phase-locked loop frequency synthesizer includes a reference route sigma-delta modulator feedback circuit, a reference phase integration circuit coupled to the output end of the reference route sigma-delta modulator feedback circuit, a phase/frequency detector coupled to the output ends of the reference and feedback phase integration circuit, a loop filter coupled to the output end of the phase/frequency detector and the input end of the reference route sigma-delta modulator feedback circuit, an oscillator coupled to the output end of the loop filter, and a feedback phase integration circuit coupled to the output end of the oscillator and the input end of the phase/frequency detector. In the phase-locked loop frequency synthesizer, the oscillator generates corresponding frequency output signals which yield the advantages of resisting noise signals, enhancing resolution, and facilitating integration.