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在锁相环里,使用扫描电路可以有效地解决加宽捕捉带和提高环路滤波能力的矛盾,但以前所使用的扫描电路都很复杂,且可靠性、有效性和通用性不很理想。近来出现的双环自动搜索扫描电路以其电路简单,工作可靠,扩捕有效,通用性好的突出优点给人们以极大的兴趣。一、老式扫描电路是怎样工作的老式扫描电路的构成如图1所示。它是由失锁指示器,控制开关和扫描振荡器三部分组成的。失锁指示器对环路的工作状态一失锁或锁定做出判决,如果
In the PLL, the use of scan circuit can effectively solve the problem of widening the capture band and improve the loop filtering ability, but the previous scan circuit is very complex, and the reliability, availability and versatility are not ideal. The recent emergence of dual-loop automatic search scan circuit with its simple circuit, reliable, expanding the effective, good versatility prominent outstanding advantages to people with great interest. First, the old-fashioned scanning circuit is how to work the composition of the old scanning circuit shown in Figure 1. It is by the lock-out indicator, control switch and scan oscillator composed of three parts. Loss of lock indicator of the working state of the loop out of lock or lock to make a decision, if