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On high-accuracy direct digital frequency synthesis using linear function approximation

This paper describes a novel design method for direct digital frequency synthesizers with very high accuracy. To this end, we leverage the well-known piecewise, multiplier-less function approximation method by two separate enhancements: A parallel function estimation scheme is applied which increases the approximation accuracy and reduces the segmentation effort. To achieve further performance improvement, gradient encoding is also taken into account. For evaluation, several direct digital frequency synthesizer architectures with varying accuracies are generated and analyzed in terms of complexity and timing. Logic and physical synthesis is performed with selected candidates. The results indicate the proposed function approximation technique as a powerful approach for the design of direct digital frequency synthesizers with spurious free dynamic ranges of 90dBc and more.