The Research Of Low Phase Niose X-band Signal Generator

Signal generator, is the key component of electronic systems. The function of the signal generator determines the performance of electronic systems. So it is also called the heart of electronic systems. With the development of modern electronic technology, the electronic systems such as radar system, microwave communication, electronic warfare, measuring instrument, guidance and biomedical engineering require high performance frequency synthesizer. The research aimed at frequency synthesizer with low phase noise, low spurious and high frequency resolution has become hot topic in the world. The research of low phase noise X-band signal generator has carried on based on this reason.Firstly, the paper clarifies the basic theory of Direct Digital Frequency Synthesis(DDS) and Phase-Locked Loop(PLL). The advantages and disadvantages of the two frequency synthesis technology are introduced. Secondly, three kinds of DDS +PLL mixing frequency synthesis and their advantages and disadvantages are presented. Thirdly, a system solution using DDS to impel PLL combined sampling mixing technology has been proposed which is based on the basic theory of direct digital synthesis technology and phase locked loop technology. In the system, a DDS is used as the clock to impel PLL, by changing the export frequency of DDS makes the export frequency keep from 25~75MHz. The reference signal tracked and locked by PLL. Above all, the system frequency is locked in 9.1~9.3GHz. In the feedback link, the sampling mixing technology is used to achieve low phase noise. A 900 MHz point frequency source is generated for the reference clock of DDS and the local Oscillator of the sampling mixer. The output of VCO and 900 MHz point frequency source mixed with the sampling mixer. The product of the mixer by the way of low pass filter, the frequency of 100~300MHz is chosen out. This four divided signal imports to the input of PLL, and when it is equal to the DDS’s output, the PLL is locked. The frequency of 9.1~9.3GHz is produced by the system. The system solution using DDS ensures high frequency resolution, using PLL achieves X-band frequency export, and using the sampling mixing technology insures low phase noise by greatly reducing N divide ratio. This article elaborates the function of each module, the distribution of indicators, the circuit design of each module and the system electromagnetic compatibility. The article focuses on the control process of MCU to DDS&PLL, the circuit design of PLL and sampling mixer and simulation design of filters.Finally, the simulation and design of all parts has been done, and the program has been written. Through the repeated debugging, the function of system has been achieved. Based on the test, the rusults can been concluded: in the range of 9.1~9.3GHz, the worst phase noise is-93.5dBc/Hz@10kHz, the spurious suppression is 45 dBc, and the frequency resolution is 16 kHz, which reached the request. It has also demonstrated the feasibility of the system solution.