# Amplifier feedback fraction and critical frequency

#### ardtuy

Joined Mar 22, 2018
5
I am unsure about a question stated as:
"An amplifier has an open loop gain of 2000 with an upper corner frequency of 500Hz. Determine the required feedback fraction to give a midband gain of 120 and determine the new corner frequency."
I found β = 1/500Hz = 0.002
Then the closed loop bandwidth of the amplifier by BWcl = BWol(1+βAol(mid)) = 2.5kHz
Then to find the the new feedback fraction I used β = 1/120 = 0.0083
I'm not sure if I should have kept the closed loop bandwidth found before and got 2.5kHz/(1+0.0083(120)) = 2.252kHz for the new corner frequency.
Is this wrong?

Joined Mar 10, 2018
4,057
GBW is a constant, so calculating the new corner trivial.

GBW = Aol x Fcorner

beta is G related

Regards, Dana.

#### ardtuy

Joined Mar 22, 2018
5
GBW is a constant, so calculating the new corner trivial.

GBW = Aol x Fcorner

beta is G related

View attachment 152097

Regards, Dana.
Thank you Dana I was going in the wrong direction. The correct method using the gain bandwidth product was right in front of me and I just didn't put the pieces together.