| DDS signal is widely used in electronic and wireless device, especially in the field of EMC test and measurement .the chapter 1 and 2 of dissertation introduce the features, typical application, key incorporated chip about DDS technology, then introduce the basic principles of DDS, especially the main elements of DDS signal generation structure.Chapter 3 and 4 is the core of dissertation; expound the innovation research result about the frequency spectrum of DDS and FM signal based on DDS.In chapter 3, non-ideal characteristics of DAC when "higher frequency DDS signal" is on is analyzed, especially the performance in DAC's Slew stage and Glitch stage, then a waveform model is constructed and it's Fourier transform is got, at last a novel analytical expression of "higher frequency DDS signal" is obtained. The experiment based on DDS IC AD9851 produced by ADI Inc, and amplitude spectrum of DDS signal is measured, demonstrating that compare with former expression, the novel expression fit measurement better.In chapter 4, this dissertation got analytical expression of spectrum of cosine modulation DDFM signal firstly. Analytical expression fit measurement by former literature well. DDFM signal contains extra harmonics comparing with standard FM signal; harmonics, especially first harmonic is the main factor of distortion of DDFM signal. Based on analytical expression, by the method of function fitting, got new approximate expression of first harmonic distortion (FHD). Compare with former expression, new expression is more precise and more applicable. As total harmonic power THP can be measured more easily than first harmonic power, dissertation THP and its deciding factors, and calculation result is showed. Based on frequency spectrum calculation, a novel measurement of distortion is defined: total fundamental distortion TFD, TFD is useful especially in the DDFM signal generator with harmonics be filtered. This paper point out that TFD is a about half of former measurement: first harmonic distortion FHD.On the other hand, effects of ADC and the DDS amplitude quantization on the power levels of the spurious spectrum are studied by computer simulation; quasi-quantitative relationship between spurs level and its deciding factors is obtained.Chapter 5 is about conclusion and prospect. We give a comprehensive summary of dissertation, and discussed the next phase of the study in two directions: the harmonic suppression filter design and modulation domain sampling theory which should be deeply developed.During the course of the study, were published 5 academic papers (including recruitment), see the Appendix List of papers. Some of innovation achievement is well received by the relevant experts. |
