The Fractional Frequency Of The Pll Frequency Synthesizer

Today , as the electronic technology is developing fantastically fast , the request for higher performance of synthesizers is put forward , wide frequency range , high frequency resolution , low jump time , low phase noise , high spurious restraining and controlled by program .These requirements are too hard to reached by using normal analog circuit . Frequency synthesizer is the key technology to produce a great deal of high resolution , high stabilization frequency signal . Fraction-N phase locked loop (FNPLL) frequency synthesizer has been appeared in recent years . It has the advantage of high frequency resolution and low phase noise when compared with traditional Integer-N phase locked loop (NPLL) frequency synthesizer . In this paper the basic theory of phase locked loop (PLL) and frequency synthesizer technology were introduced , the theory and implement of FNPLL frequency synthesizer were discussed too . Loop filter is the key component to keep frequency synthesizer working steadily and outputting signal of excellent performance . In this paper methods of designing loop filter were given . the reliability were verified in experiment .