Based On The Dds Sweep Signal Generator

The Direct Digital Frequency Synthesis(DDS) is a new frequency synthesis method and also a revolution in the frequency synthesis technique.The fully digital DDS technique has such advantages as high frequency resolution, fast frequency switching speed, low phase noise and high stability. And it outshines other frequency synthesis methods. With an intensive study of digital integrated circuit, microelectronics and EDA technology, DDS is developed at speed.The theory of DDS is gone into in the paper firstly. According to the composition of DDS, the time - domain expression is derived. The spectrum analysis is made in the frequency - domain, and some rules are simulated with Matlab. And three factors which result in frequency stray are analyzed. In the end some classical methods which help to eliminate the stray are summarized.Sweep signal generator is a device that generates excitation signal. The design of the sweep signal generator based on DDS is carried through mainly in the paper. And the generator has two ways in the frequency output: sweep and dotted. It also possesses other functions, like frequency measurement and sweep speed control.The system consists of hardware and software. And the hardware part is composed by CPU(AT89C52), CPLD of Lattice corporation, the digital / analog converter, low pass filter, keyboards and LED display, and so on. The modular programming approach is adopted on the software design and code is writed in C51 language.According to the EDA development flow, CPLD is programmed in Verilog HDL language to realize DDS. Because of the use of Lattice's CPLD, the design of digital system is finished in the integrated development environment: ispDesignEXPERT and all modules are synthesized with Synplify Pro7.3. The design accords with requirements fully.The theoretical research in the paper will have important instructing signification on designing DDS of high precision and low noise.Based on the theory, DDS is realized with CPLD through program and the design of sweep signal generator is finished. And the system will have high price performance ratio.