本文分析了数字锁相环路的寄生频偏,它是现代通讯系统中频率合成器的重要指标之一。文中首先计算了一种取样保持鉴相器的取样纹波,其次引用文献[5]关于正弦波加随机噪声的一般理论,分析了锁相环路寄生频偏的随机特性,得出了在考虑取样纹波与噪声同时影响下寄生频偏的概率密度曲线和估算寄生频偏的公式,最后列出了寄生频偏概率密度的测量结果。 This paper analyzes the frequency offset of digital PLL, which is one of the most important indexes of frequency synthesizer in modern communication system. In this paper, we first calculate the sampling ripple of a sample-and-hold phase detector. Secondly, referring to the general theory of sinusoidal plus random noise in reference [5], we analyze the random characteristic of the parasitic offset of PLL. The probability density curve of the parasitic offset and the formula of estimating the parasitic offset are simultaneously affected by the sampling ripple and noise. Finally, the measurement results of the probability density of the parasitic offset are listed.