Design Of Signal Generator Based On Direct Digital Frequency Synthesis

Signal generator is a device which can provide the signal of a variety of frequencies,wave-forms, and output levels. As an important electronic device, It not only greatly improves the efficiency of users, but also gets the attention of many researchers. In communication, electronic warfare, navigation and instrumentation, and other fields,it has a wide range of needs and development prospects. The third generation frequency synthesis---direct digital frequency synthesis technology, which achieves frequency synthesis in an all-digital way.DDS Technology has many advantages far beyond the traditional frequency synthesizer technology in frequency conversion time, frequency resolution, phase continuity, the relative bandwidth and integration, and many other performance parameters. With the development of large scale integrated circuits and high-speed digital signal processing technology, DDS technical superiority is increasingly obvious, getting large scale application and promotion. This paper analysis the design of signal generator based on DDS technology. The main content is summarized as follow:This paper analysis DDS technology detailed, not only at the basic principles and the basic structure, but also factors of non-ideal spectrum and so on. At the base of this, this paper proposed signal generator system architecture based on DDS, and made a brief description of the function of each module.In the phase accumulator module, accumulator speed directly determines the performance of the overall system. This paper introduced the "pipeline" structure achieving cumulative function module in order to improve efficiency. For the high resource consumption of traditional "pipeline", this paper further proposed improvement measures,using the new pipeline architecture "pipeline-timing" to control and reduce the resource waste of the system.This paper proposed a design scheme of ASK(amplitude shift keying), FSK(frequency shift keying), PSK(phase shift keying), and CDMA(code division multiple access)based on DDS technology. At the same time, this paper completed the design of the raised cosine filter circuit, in order to overcome the phenomenon of inter-code interference, which occurred during the signal generator design process. Exploiting the adder tree structure, made the raised cosine filter with the advantages of consuming fewer resources, fast computing speed.The circuit design of signal generator based on DDS technology in this paper was implemented with the Xilinx FPGA Virtex-5 family XC5VLX155 T using Modelsim completing function simulation, and using ISE completing the circuit synthesis, placement and routing. The result of producing wave-forms is very satisfied, and filter achieves the intended design indicators: center frequency of 40 MHz, bandwidth of 10 MHz, out of band signal suppression ratio of 30 d B.