Wideband Low Spurious Dds Signal Generator

Frequency synthesizer,heart of the electronic equipment,has been widelyapplied in many fields such as communication, radar, electronic counter, navigation,broadcast, remote controlling and measuring and instruments. It is a very importantpart determining the performance of electronic systems. DDS (Direct DigitalFrequency Synthesis) is a new frequency synthesis technology coming after directsynthesis and PLL synthesis. DDS is a wholly digital structure circuit with variousadvantages such as fast frequency switching speed, high frequency resolution, lowphase noise and maintaining constant phase while frequency hopping. In the recentdecade, it has been widely used and a rapid progress has been made on it. For thelimitation of digital hardware operating speed, Nyquist theorem and DDS'structure,the spurious performance of DDS'output is bad and the output frequency can't reacha high level.In this dissertation, a systematic research is made on DDS. Firstly, thedevelopment of the frequency synthesis is introduced. The output spectrum of theDDS on the presence of both phase and amplitude truncation is analyzed. Ananalysis is also made on the effect of the DAC's nonlinearity. Based on analyzing theoutput spectrum of the DDS, some methods to reduce spurs are proposed. They aremodified Nicholas phase accumulator, random dithering and Rom compressingtechniques. Then a sine/cosine generator based on CORDIC algorithm is researched.A new structure of DDS is formed by substituting the ROM in DDS with thesine/cosine generator. In this structure, the spurious performance is no longerrestricted by the capacity of the ROM. Finally, combined with the practicalengineering, the controlling circuit panel of the low spurs and wideband DDS signalgenerator is developed.