基于分段非线性函数近似的直接数字频率合成器

Direct digital frequency synthesis based on piecewise continuous nonlinear function to approximate

对直接数字频率合成器(DDS)中的相位幅度转换模块提出了一种基于分段非线性函数近似的的设计方法。这种方法取代了传统的ROM查找表的方法,可以避免因采用大容量的ROM而带来的成本高、功耗大、可靠性下降等缺点。此方法对正弦函数的第一象限进行分段,在每一段内用非线性函数近似,然后再根据正弦函数的对称性质,重构完整的正弦函数。此法可以获得较好的压缩效果,并且结构简单,易于实现。

This paper presented a method which based on piecewise continuous nonlinear function to approximate the sine function for direct digital frequency synthesis. Compared with look up table, this method can avoid cost of DDS increase, high power, reliability drop brought by large capability of read only memory （ROM）. First quadrant of sine function is divided, then nonlinear function approximates sine function in each segment. According to symmetry character, integrated sine function is reconstructed. This method achieved good compression ratio, simple architecture, facile realization.