改善DDS输出LFM信号谱质的方法

A Method for Improving LFM Signal Spectrum Quality in Direct Digital Synthesis

分析了直接数字合成的相位截断杂散、幅度量化误差杂散和DAC非线性杂散的分布规律。根据这些噪声分布特点,提出了一种利用设计合理的外围电路和选择合理的控制字的方法,提高了直接数字合成技术产生的线性调频信号的频谱纯度,并用直接数字合成芯片AD9854设计了线性调频信号合成器。实验结果表明,用该方法产生的线性调频信号在带宽达30MHz时,无杂散动态范围达到了62dB,改善了近10dB。

In this paper, the distributing rules of spurs in the DDS output spectrum is analyzed. A effective method to design reasonable external circuits and choose appropriate instruction words is presented to improve the spectrum purity of the LFM signal. DDS chip （AD9854） is used to generate a broad band LFM signal. The experiments result shows that the LFM signal can achieve 62 dB SFDR with using this method in 30 MHz bandwidth, It increases the SFDR in about 10 dB than that without using this method.