小步进频率合成器的设计

Design of a Small Step Frequency Synthesizer

回顾了三种基本的小步进频率合成器设计方法的优缺点。介绍了一种特殊的小步进频率合成器的设计方法 ,即采用两个大步进频率的单环锁相电路混频 ,两者步进频率的差较小为r ,就能获得输出为小步进频率 (为r)的合成器 ,并给出了相应的理论依据和计算。只要合理设置频率 ,规避互调分量的影响 ,就能使合成信号保持大步进频率单环锁相电路较低相位噪声、较短跳频时间和较低杂散信号的特性 ,而且合成原理简单 。

This paper reviews three basic techniques suitable for small step frequency synthesizer, along with their advantages and disadvantages. A special design method for small step frequency synthesizer is presented, namely frequency synthesis using two single loop PLL with large frequency step combined together. T heir frequency step difference is small i.e. r. The combination can produce an output with small step size(as r ). Theoretical analysis and calculation is presented. If the frequency is set correctly to avoid the influence of the intermodulation products, characteristics of low phase noise level and short hopping time and low spurious signals level in single loop PLL with large step size will be maintained. The principle of frequency synthesis is simple and little circuit adjustment is needed.