Analysis on Using DDS as a Digitally Programmable Fractional N Divider in PLL
Sun Hua · Radio Engineering of China · 2009
Some commonly used frequency synthesis methods are introduced first,and then the characteristics of direct frequency synthesis,indirect Phase Locked Loop(PLL)synthesis and DDS+PLL synthesis are described.The method with DDS working as a digitally programmable fractional N divider in PLL is discussed particularly.Its operation principle and critical technologies are analyzed in detail.After analyzing the causes of spurious of DDS,the design method of DDS filters is discussed and a directive conclusion is drawn.The experimental result which proves the validity of this method is presented in the end of this paper.