Research Of Spurs Reduction Of Direct Digital Frequency Synthesizer

The emergence of direct digital frequency synthesis (DDS) bring about a revolution of frequency synthesizer technology, it is widely used in instrumentation, radar, communication and other fields. With the project background "DDS Function Generator", a lot of work has been done which is aimed at the defect of DDS that spurious signal is strong.To research the reduction of spurs better, it is necessary to analyze the source of spurs in detail. This thesis first introduces the basic structure and operating principle of DDS. Then, a detailed analysis of the spectrum is given, when DDS works in the ideal case, works with phase truncation, and works with quantization error. For these three kinds of situations, the flow of spectral analyses is that Matlab simulation could be done only after mathematical derivation. When analyzing the effect of phase truncation error, an accurate mathematical model is built after referencing Nicholas’s article. When analyzing the amplitude quantization error, this thesis introduces the Bessel function for the first time, so that the result becomes more intuitive.For these years, a lot of technologies about how to reduce the spurs has been proposed by scholars at home and abroad. This thesis selects three technologies to research. They are phase accumulator improving technology, phase dithering and noise shaping technology. After a detailed theoretical analysis and Matlab simulation, these three technologies are implemented using circuit module that can be integrated. In the process of testing, the jitter injection technology and noise shaping technology are both adjusted appropriately to obtain good results.Besides the research of spurs, improvement of other special signals has also been done. On the one hand, this thesis improves the AM algorithm and FM algorithm, which are simpler and more efficient. On the other, the square’s double shadow is studied for the first time, and a new square algorithm is introduced, which weakens the suqare’s double shadow effectively.Test results show that the spectrum diagrams got in test are close to Matlab simulation results, which verify the correctness of related theory. Meanwhile the wideband SFDR is improved a little, about2.52dBc is improved.