DDS线性调频信号时钟抖动误差分析

Analysis of Clock Jitter Error in LFM Waveforms Based on DDS

直接数字频率合成(DDS)是产生线性调频(LFM)信号常用方法,时钟抖动是影响其信号质量的因素之一。从时域出发,建立了由时钟抖动引起的DDS输出误差模型,推导出了抖动引起的LFM信号信噪比理论预测公式。分析指出随着时钟频率的提高,时钟抖动对信噪比的影响更加明显;当时钟抖动低于10ps时,信噪比对时钟抖动的变化更为敏感。针对给定的信噪比要求和确知的LFM信号,给出了时钟抖动的限定公式,设计者可据此选择恰当的时钟源。最后,通过实验验证了理论推导的正确性。

DDS is a frequently used method to generate LFM signal, in which clock jitter is one of the major factors that affect signal quality. Clock jitter error model in DDS is proposed, and the forecast formula of SNR of LFM signal caused by clock jitter is derived in the time domain. Analysis reveals that the effect of jitter to SNR is more dominant as the clock rate increases, and the SNR is more sensitive to jitter when the RMS jitter is less then 10 ps. The formula of jitter limitation is presented for desirable SNR and determined LFM signal, which ensures the designer to choose clock source appropriately. Finally, the validity of the theory analysis is proved by the experiment.