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本文分析二阶锁相环当无用信号加于有用信号时的性能。这两种信号都是正弦且未调制的信号,分析是在没有附加噪声的情况下进行的。当环路仍锁定在有用信号时,在鉴相器的输出端就有寄生信号。这种信号使压控振荡器(VCO)产生寄生调相,并在环路中有静态相位误差。本文估算了寄生信号幅度、寄生调相指数和静态相位误差,给出了使环路保持锁定的所需条件。环路开初未锁定,根据这两种信号的幅度比和频差的大小,可能锁在有用信号上,也可能锁在无用信号上。得出了一个计算牵引时间的公式,当环路锁在有用信号上时,捕获可快于或慢于没有有用信号时的情况。当环路锁在无用信号上时,也会看到同样的现象。
This paper analyzes the performance of second-order phase-locked loops when unwanted signals are added to useful signals. Both signals are sinusoidal and unmodulated and the analysis is done without additional noise. When the loop is still locked in the useful signal, there is a parasitic signal at the output of the phase detector. This signal causes a voltage-controlled oscillator (VCO) to generate a parasitic phase and a static phase error in the loop. This article estimates the parasitic signal amplitude, parasitic phase index and static phase error, giving the necessary conditions to keep the loop locked. The loop is not locked at the beginning. Depending on the amplitude ratio and the frequency difference between these two signals, the loop may lock onto a useful signal or lock onto a useless signal. A formula for calculating the pull-in time is derived and can be captured faster or slower than when there is no useful signal when the loop is locked on a wanted signal. The same thing happens when the loop is locked on a useless signal.