The Research And Realization Of Frequency Synthesizer Based On DDS And PLL

Frequency synthesizer is one of the most important parts in modern communication and electronic system. With the development of modern communication techniques, frequency synthesizer is required to have higher performance such as wide band, fast frequency switching speed, low phase noise, pure output spectrum, high resolution etc.In order to implement frequency synthesizer with high performance, the basic implementing theory of frequency synthesizing is studying. Considering the advantages of the combination of DDS and PLL and the required parameters of frequency synthesizer implemented, we adopt the scheme in which DDS is employed to drive PLL.High performance DDS chip, labeled AD9850, is select to generate the reference frequency between 7MHz and 10MHz.The resolution of the reference frequency can reach to 1Hz. The PLL can generate tenfold frequency of the reference frequency for satisfying the requirement of the system with lower spurious and high output power.At last the hardware and software modules of frequency synthesizer are developed. The required parameters of designing frequency synthesizer can be satisfied. The output frequency is 70MHz～100MHz, the output power is +7dBm～+10dBm, the spurious is better than 70dB.