Filter Group delay 和 step response關係

s20192s20192

最近在看Filter相關書籍
書中提到
1.
The time for the step response to reach the value 0.5 is an approximate measure of the average group delay
3 |1 c+ {6 h1 X9 B; {and ringing in the step response indicates that the group delay varies strongly in the passband
1 ]: u: ~! i3 M" H' c# P9 V) u想請問為何從step response中就可以知道關於group delay
有什麼相關數學公式來驗證這些關係嗎

4 [3 F% n) _) r# b# d2.
voltage mode and current mode
6 c' x+ H' X, J9 n& P! G為何voltge mode較不適用在高頻阿
書中是說voltage mode 用 feedback
所以較不適用在高頻
但是用回授
不是頻寬增加!?

想請教版上各位大大這兩個問題

/ m( X7 F% Q* G$ X' _+ r$ H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
- _- ~5 U& }' E" A5 K: k
感謝