Study Of Fractional-N Digital Phase Locked Loop Frequency Synthesizer

The development of modern technology brings more and more difficult requirement for signal source. The output of signal source must have wide frequency range,high frequency resolution,low phase noise,high spurious restraining and can be 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 frequency signal. It has been an important component of communication,radar,instrument,high-speed computer and navigation equipment.Fractional-N phase locked loop (FNPLL) frequency synthesis 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 synthesis. But this excellent technology has not been used widely in practice. In this paper the author introduce the basic theory of phase locked loop (PLL) and frequency synthesizer technology,and discusses the theory and implement of FNPLL frequency synthesizer. Loop filter is the key component to keep frequency synthesizer working steadily and outputting signal of excellent performance. In this paper,author proposes a practical method for loop filter,and verifies its reliability in experiment. At last,the difference between FNPLL and NPLL frequency synthesizer's performance is discussed and analyzed theoretically,and it is testified in the experiment.