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The overall operation of a direct digital frequency synthesiser (DDFS) is based on a look-up table method, which performs functional mapping from phase to sine amplitude. The spectral purity of the conventional DDFS is determined by the resolution of the values stored in the sine table ROM. However, large ROM storage means higher power consumption, increased silicon area, lower reliability, lower speed and increased costs. A novel systematic design methodology for implementing a DDFS architecture with reduced memory size is introduced. Describing the proposed architecture using the hardware description language VHDL, it is possible to generate a plethora of alternative realisations in terms of the number of input and output bits, the memory size, the number of gates, the memory segmentation parameters and the spectral purity. In other words, the designer can perform extensive architecture exploration to reach an optimal solution. The experimental results prove that the new DDFS architecture can be realised with a smaller hardware complexity and total power consumption and improved performance compared to many existing approaches.
Date of Publication: August 2007