现代频率合成中的锁频环实验研究

压控振荡器（VCO）是合成器中的关键器件之一，其噪声特性直接影响合成器的相位噪声和环路动态特性。在锁相合成器中，特别是宽带合成器中，对VCO采用附加锁频环进行稳频控制，明显地优化了合成器载频中远区的相位噪声，锁频环已成为先进合成器的关键技术。该文描述了锁频环（FLL）的原理，对锁频环的环路特性和相位噪声进行了理论分析，并以C波段合成器为例，给出了常规小数锁相环和小数锁相附加锁频环的实验研究结果。实验证明锁频环对优化合成器中远区相位噪声效果明显。

Experimental Research of Frequency-Locked Loop for Modern Frequency Synthesizer

VCO is a key element in frequency synthesizer,and its noise influences phase noise and(dynamic) characteristic of frequency synthesizer directly.In frequency synthesizer,especially in wideband(synthesizer,) phase noise at the middle-far band from carrier frequency will be improved effectively by adding a frequency-locked loop(FLL) to VCO.The FLL has become a key technology in advanced frequency synthesizer.In this paper,the operational principle of FLL is described,its loop characteristic and phase noise are analyzed and discussed.At last,taking a C band frequency synthesizer as example,the experimental results of the fraction-N phase locked loop(FNPLL) and the FNPLL added with FLL are given,the experiment proves that FLL improve clearly the synthesizer phase noise at middle-far band.