| With the development of radio technology, the communication system is raising the ever-increasing demands for the signal fidelity, frequency accuracy and amplitude stability, while the signal generator which is the essential component of the communication system determines the outcome of the systems to a large extent. Meanwhile, frequency synthesis technique makes new breakthrough because of the mushroom growth of computer and micro-electronics technology, and then the theory of direct digital frequency synthesis (DDS) is proposed. DDS has many obvious advantages such as high frequency-agile speed, wide relative bandwidth, high frequency resolution, continuity of output phase, programmable and all-digital architecture that is easy for monolithic integration.This article presents a method of the design and implement of mutil-mode siginal generator based on the technology of software defined radio (SDR) and DDS.Firstly, the growth of frequency synthesis technology is analyzed, and the value of multi-mode signal source is illuminated. Then the basic principle and structure of DDS is introduced, and the DDS signal stray is studied in detail. Then the main methods of overcoming signal stray are raised, such as fitting of swallowing pulse signal, compression of ROM capacity, CORDIC algorithm.After that the paper briefly introduces the overall structure and main application chips of the signal sources, and on this basis, puts emphasis on software architecture and design concept, and gives a serious analysis of design approach of the simulation and digital modulation especially frequency-hopping mode. Meanwhile, a general quadrature modulation model is put forward on the basis of research of previous signal processing algorithm, namely the signals of various modes can be converted into common orthogonal model to achieve. The NIOS II softcore processor is successfully used in FPGA logic design so that the goal of using FPGA implementing signal processing is achieved. |
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