[問題] 一個有關stability的問題
請教各位大大
我們在電子學分析穩定度通常會採用Barkhausen's Criteria
也就是利用phase margin和gain margin去測試一個系統的穩定度
通常認為一個open loop系統在unit-gain bandwith之內有兩個以上的pole的情況下
則表示系統在相位180度時還會有大於1的增益 有可能造成系統變成正回授而不穩定
但是我們一般在設定高階濾波器時為什麼都沒有在考慮系統的phase margin呢?
例如我要設計一個3-order的active low-pass filter時open loop就會有三級積分器
如此一來 phase margin勢必不夠
為什麼像高階filter這樣phase margin不夠的loop可以穩定呢?
換句話說 保證沒有pole在右半平面和phase margin之間的關係是什麼呢?
感謝回答!
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