带通限幅器对锁相环噪声性能的影响

锁相环路中,在鉴相器前加上AGC（自动增益控制）,可以使环路性能在输入信噪比发生变化时保持稳定,带通限幅器也可以起到类似作用。尽管有一些文章对限幅器的性能作了研究,但是在PLL（锁相环）闭环条件下,鲜有文章分析其对环路噪声性能的影响。因此,文章以基本PLL环路的数学模型为基础,推导出PLL中分别加入相干AGC和带通限幅器后新的环路数学模型,以一阶PLL为例,计算和比较不同控制方式下环路相位误差均方值的变化,最后说明应当根据飞行任务的不同选择对环路更有利的控制方式。

Effects of Band-Pass Limiter on PLL Performance in Presence of Noise

Use of AGC(Automatic Gain Control) before the phase detector in a PLL(Phase-Locked Loop) stabilizes the loop during variation of the input SNR(Signal-to-Noise Ratio).A band-pass limiter has a similar function.Little research is done on the impact of the limiter on the noise of a closed PLL among existing literature on the performance of band-pass limiters.Based on generalized PLL model,new mathematical models are derived with coherent AGC and band-pass limiter in the PLL.Taking first-order PLL as an example,variation of phase error variance in different control modes is computed and compared.It is finally pointed out that a control mode more favorable to the loop should be selected for different choices of flight missions.