一种新的正交直接数字频率合成器设计方案

Novel Approach to Designing Quadrature Direct Digital Frequency Synthesizer

为了提高正交直接频率合成器输出频谱纯度和降低逻辑单元占用率,提出了一种新的分解二阶多项式近似算法。这种算法是将正(余)弦函数分解为几个相关函数,进行二阶多项式近似。与传统二阶多项式近似算法相比,该算法输出频谱纯度较高,无杂散动态范围(SFDR)可达到99.3dBc;该算法所占用的逻辑单元比二阶多项式近似算法减少20%。实验表明,在设计高频谱性能的正交直接数字频率合成器(Quadrature-DDFS)方面,该算法具有明显优势。

A decomposition method for parabolic polynomial approximation was proposed to improve spurious free dynamic range （SFDR） of quadrature DDFS （Direct Digital Frequency Synthesizer） and decrease logic element occupancy. In this technique, sine （cosine） function was decomposed into several correlation functions, which was then calculated by using quadratic polynomial approximation. Compared to the conventional quadratic polynomial approximation, the proposed method could achieve a higher SFDR （up to 99.3 dBc） and a 20% reduction of logic element occupancy. Simulation results showed that, in high spectral quadrature-DDFS design, the proposed method is significantly superior in hardware cost, compared with the conventional approach.