抖动处理对DDFS合成波形频谱的改善

实际的DDFS系统中,由于波表(WFT)宽度和深度的限制,会带来幅度上的舍入误差和相位上的截断误差.舍入误差在频谱中的接近白噪声,而相位截断误差在频谱上表现为一个个独立的谱线.针对相位截断误差的特点,采用相位数据加入抖动的方法可以对合成波形质量加以改善.仿真表明,采用适当的抖动处理后,合成波形的无杂散动态范围(SFDR)得到10 ～20 dB的改善;在一定的WFT深度下,随着加入抖动信号幅度的变化,合成波形的SFDR有一个最大值.意味着在一个基本DDFS系统中,可以用很小的硬件开销就可以得到10～20 dB的波形质量改善.

Dither Rendering: The DDFS Spectral Purity Improvement

In DDFS system, the finite capability of waveform table lead to the phase truncation error, and the finite word length result in the rounding error. The spectral distribution characteristic due to the phase truncation and rounding are different. The spectral density caused by phase truncation can be spread out by rendering dither to the input of waveform table. The simulation showed that the broadband noise are increased, but the SFDR of synthesized wave can be improved by 10-20dB.