| With the development of digital integrated circuits and microelectronics technology, direct digital frequency synthesis technology shows its superiority gradually. Direct Digital Synthesis (DDS) is made up of the phase accumulator, the sine look-up table, the digital to analogy converter and the low band filter, which has many advantages, e.g. high frequency resolutions, fast frequency switching speed, low phase noise, the ability to switch frequencies while maintaining constant phase and the ability to producing arbitrary waveforms. Now this technology has been widely used in the field of radar, communication, apparatus, etc.The thesis compares the ideal features of various frequency synthesis technology and analyzes some information including spectrum of output signal and related technology indicator. The paper mainly uses the high-performance ARM microprocessor to control AD9859 which can achieve the designated frequency output, and realizes the modulation of frequency, phase and scope modulation. The thesis confirms the programs of hardware and software and divides the whole system into some parts, such as control module, DDS module, LCD display module, filtering module and communication module. It carries the function requirement of this design into effect. The master module controls DDS, LCD and keyboard by using ARM chip LPC2138 and FPGA coprocessor. This master module has excellent operability. In filter part a seven-order elliptic filtrator is designed to filter spurious signals of DDS so that we can obtain a better output frequency characteristics. We use FPGA to do high-resolution frequency measurement, which achieves the real-time display of output frequency.Finally, through analyzing the practical testing results, this paper summarizes the influence of output wave which was caused by the changes of DDS input reference frequency and internal PLL clock multiplier factor. The conclusion provides valuable experience for the following researches of this project. |
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