Filter Group delay 和 step response關係

s20192s20192

最近在看Filter相關書籍
書中提到
1.
! D0 G5 {. e9 ~The time for the step response to reach the value 0.5 is an approximate measure of the average group delay
7 D/ G7 A  G1 U/ {3 Aand ringing in the step response indicates that the group delay varies strongly in the passband
想請問為何從step response中就可以知道關於group delay
/ o" T3 c' y& E' w有什麼相關數學公式來驗證這些關係嗎
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$ Q7 P; @8 \5 p- _2.
voltage mode and current mode
5 C) A; C! E* \8 ], e為何voltge mode較不適用在高頻阿
4 K0 ^, Y7 o& H1 h$ h/ |書中是說voltage mode 用 feedback
( R6 f9 s$ V8 O" `; x8 ~; t% `; K所以較不適用在高頻
但是用回授
不是頻寬增加!?
5 L; Y8 N: e: ?
想請教版上各位大大這兩個問題
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感謝

s20192s20192

再多補充一個問題
為何group delay (in passband)為何會隨頻寬減少而上升阿
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感謝