The Design Of DDS Signal Generator Based On FPGA

The technology of Frequency Synthesis, which consists of Direct Synthesis, phase-locked Synthesis and Direct Digital frequency Synthesis (DDS), is widely used in the area of communication, aeronautics and instrument, ect. The Direct Digital Frequency Synthesis is a kind of new frequency synthesis method and also a revolution in 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.DDS is a method that can transform the digital signals into analog signals by means of DAC. With the help of the high-speed ROM which is used as a look-up-table, the sin-waveforms or other waveforms can be obtained by using the high-speed DAC. The common DDS is composed of three parts: the Phase Adder accomplishes the accumulation of the phase; the Phase Code-Amplitude Code Transformer is realized by ROM; the DAC transforms the digital signals into analogy signals.Field Programmable Gate Array (FPGA), because of its flexible designing and high speed, has been used more widely in digital ASIC. The paper mainly discusses how to realize a DDS system with FPGA. The hardware of the design is Cyclone series FPGA made by Altera Inc.The paper firstly introduces the development of frequency synthesis techniques, and discusses the significance of realizing the direct digital frequency technique based on FPGA. Secondly, the principle and structure of DDS are introduced, and a few knowledge of FPGA such as the structure, peculiarity, design flow and design tools are introduced. Then the paper introduces the principle, the circuit diagram and the optimization method of realization DDS based on FPGA. The importance of how to realize DDS through FPGA is introduced, and some VHDL code is given. Above all, this DDS system possesses some characteristics including high performance, high proportion between price and performance and simple circuit diagram, and so on. It can be embedded into other system easily without special DDS chip. Thirdly the paper analyses the spectrum characteristic of direct digital frequency synthesizer output. Especially, the spectrum characteristics of the phase truncation error and amplitude quantization error are discussed at length, and some methods of how to improve the performance of the system are presented. At last, it has given the picture of the hardware circuit and the test result, and some analysis is made for it.