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发表于 2024-7-17 08:20:40
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本帖最后由 sunjimmy 于 2024-7-17 08:21 编辑
負回授的環路內, 耦合進環路內的訊號(干擾源),均會被環路增益衰減.
for example:
input: X
output: Y
open-loop gain=A
feedback ratio=B
=> closed-loop transfer function, Y=X*[ A/(1+A*B) ]
assume there is noise injected (coupled), n, at output
A*[X-B*Y]+n=Y
=> closed-loop transfer function, Y=X*[A/(1+A*B)] + n*[1/(1+A*B)]
從上式可見, n 被衰減(1+A*B)
環路增益 ,(A*B), 頻寬定義了PLL帶寬. 帶寬外環路增益小於1
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