Research And Implementation Of Wideband High Resolution Frequency Synthesizer

With the rapid development of science and technology, electronic measuring instrument such as spectrum analyzer, take the more and more highly request to the frequency sources. The broadband high-resolution frequency synthesizer has been widely concerned. In this paper, two kinds of scheme are adopted to achieve the broadband high-resolution frequency synthesizer: one is DDS driving PLL circuit structure; the other is the frequency synthesis technology based on sigma-delta modulator. However, there are stray problems in these two solutions, the inhibition of stray become their common tasks. This paper pays essential attention to focus on stray problems in two solutions and put forward the methods to suppress the spurious.Firstly, this article carried out research on the issue of DDS spurious, especially the spurs introduced by the phase truncation and proposed a new method to suppress the spurious. Then, some commonly combinations of DDS/PLL are discussed in this paper and the method that DDS driving PLL is proposed in this dissertation. This paper designs the core circuit composed by DDS, phase lock,loop filter etc. In order to suppress the spurious, this article improves the classic DDS driving PLL scheme by introducing the regulatory factors. Test results show that the design requirements such as phase noise, frequency resolution and spurious suppression are fulfilled.Finally, this paper analyzes the Fractional-Spurs in frequency synthesis scheme based on the sigma-delta modulator and a new method to suppress the Fractional-Spurs is proposed. This paper analyzes the DSM and the MASH structure, then confirms the structure of MASH series and data width. Inspired by a DDS structure, a new method of suppressing spurious is proposed in this paper. The simulation and formulas shows that the new MASH structure could effectively restrain the Fractional-Spurs for all input constants and initial state. In order to verify the effectiveness of the new MASH structure, the fractional-N divider with the proposed MASH structure is completed on an existing frequency synthesizer. Extensive testings shows that, in the range of frequencies of 3.74GHz to 8.96GHz, the resolution is much better than lHz, band spurious is better than-80dBc, and the phase noise is better than-95dBc/Hz @ 10 KHz.