L波段FH频率合成器的设计与实现

Design and Realization of L-Band FH Synthesizer

设计具有快速频率捷变与低相位噪声性能的 L波段 FH频率合成器 .利用 DAC电路对 VCO控制电压进行快速预置 ,大大缩短了频率捷变时间 .优选环路分频比 N值和参考分频比 R值 ,使输出频率与 N值呈非线性关系 ,即采用非等间隔跳频方式 ,有效降低了因环路分频比 N过大的输出相位噪声 .当参考源使用普通晶体时 ,测量结果表明 :频率捷变时间 <10 μs,输出单边带相位噪声谱密度约为 - 70 d B/ Hz(偏离载频 1k Hz)

An L band frequency hopping synthesizer that is provided with performances of fast frequency hopping and low phase noise was designed, the project of fast pre setting to VCO by DAC circuit was adopted, and a very short frequency switching time was got. Through optimizing loop division factor N and reference division factor R , making output frequency of FH synthesizer have a non linear relation with loop division factor N , namely adopting frequency hopping with non uniform frequency step,the output phase noise caused by bigger N can be reduced. When a general crystal was used in reference frequency source, the result of measurement is as follows: the frequency switching time is less then 10 μs, the output SSB phase noise spectrum density is about -70 dB/Hz at 1 kHz offset.