How does someone can come to this formula in closed loop OpAamp?

Thread Starter

TarikElec

Joined Oct 17, 2019
115
Hello Everyone,
SO I found this amazing article (part 2) about negative feedback and I love it. how does he come to that the

closed-loop cutoff frequency (fC,CL) is related to the open-loop cutoff frequency (fC,OL) as follows:


fC,CL=fC,OL(1+ALFβ)
 
Last edited:

Papabravo

Joined Feb 24, 2006
21,159

LvW

Joined Jun 13, 2013
1,752
However, you should keep in mind that this simple relation between open-loop (Aol) and closed-loop (Acl) bandwidth is valid only under the assumption that the open-loop frequency response Aol (magnitude) can be regarded as a 1st-order system only (20dB drop below the unity-gain frequency (Aol=0dB).
 

Thread Starter

TarikElec

Joined Oct 17, 2019
115
This derivation of the closed loop transfer function can be found in elementary textbooks and articles on feedback control. Like this one:
https://www.electronics-tutorials.ws/systems/closed-loop-system.html#:~:text=To find the transfer function of the closed-loop,equal to: Output = G x Error
Thanks, but I could not find on the link you attached, the frequency bandwith of closed loop in term of the open loop bandwith and the gain as : fC,CL=(fC_OL)*(1+AL*Fβ)
 

Thread Starter

TarikElec

Joined Oct 17, 2019
115
However, you should keep in mind that this simple relation between open-loop (Aol) and closed-loop (Acl) bandwidth is valid only under the assumption that the open-loop frequency response Aol (magnitude) can be regarded as a 1st-order system only (20dB drop below the unity-gain frequency (Aol=0dB).
thanks, this I did not knew
 
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