The Dds-based Broadband Low Spurious Quadrature Signal Generator

Direct Digital Frequency Synthesis(DDS),as a new kind of frequency synthesis method,is a revolution of frequency synthesis technology .With the development of digital integrated circuits and microelectronic techniques, DDS exhibits its superiorities day by day. It has been more recognized as the best method to generate sine wave, LFM and other complex signals, and has been used widely in radar system.Modern radar not only gains the information of position and speed of the objects, but also analyses and distinguishes the objects, which requires the signal with a wide band emitted by radar to gain the high resolution of distance and other characteristics of objects. So it has become an important requirement in designing a radar signal generator that generating radar signal with wide band even ultra wide band. The main content of project is designing an I/Q signal generator with wide band and low spur.Firstly the dissertation introduces the course, modern situation and development trend of frequency synthesis techniques, and compares with the characteristics of different frequency synthesis techniques. Secondly, the principles, structure, and functions of every part are introduced, and then the advantages and disadvantages are also analyzed. In the 3rd chapter, the spectrums of output spur both in ideal and actual parameters are deduced, especially, the spectrum characteristics of phase truncation error, and the simulation in Matlab and theoretically the solutions are followed. As the important chapter, the 4th chapter puts forward the whole scheme on the basis of analysis of DDS.This project selects AD9858 as the core chip, controlled by FPGA after comparing with DDS chips of several companies, and designs the scheme of circuit and PCB. AD9858 is an extraordinary powerful DDS chip, which not only has all the advantages of general DDS, also has advantages of wide band and low spur, bringing more conveniences in the processing of the design. Finally, the 5th chapter clarifies some problems in software and hardware met in the testing, what's more,it also put forward some own opinions and solution in the design. As a result, all the parameters of the signal accord with the demands.