# Can someone help me find the closed loop gain

#### ytimk1974

Joined Oct 4, 2013
6
This is a question that I just can't seem to find the answer for in my text:

Given that open loop critical frequency = 750Hz, the closed loop critical frequency = 5.5kHz, and the A'ol = 89dB, determine the closed loop gain in dB.

Anybody's help is greatly appreciated.

#### LvW

Joined Jun 13, 2013
1,478
Please, can you explain to us the term "critical frequency"?

#### ytimk1974

Joined Oct 4, 2013
6
Well I was hoping someone would understand that because I have been over every formula in this text and can't come up with any formulas that need these specific numbers. I'm sure I am missing something. The definition in the glossary says that it is the frequency that defines the end of the passband filter; also called cutoff frequency.

#### WBahn

Joined Mar 31, 2012
26,871
Well I was hoping someone would understand that because I have been over every formula in this text and can't come up with any formulas that need these specific numbers. I'm sure I am missing something. The definition in the glossary says that it is the frequency that defines the end of the passband filter; also called cutoff frequency.
If the approach you take to learning electronics is to pour over lists of formulas looking for one that needs the specific parameters that you've got, then you are going to have lots of problems.

What you are missing is comprehension of the material you are studying.

Try looking up "gain-bandwidth product" and see if it sheds some light.

#### ytimk1974

Joined Oct 4, 2013
6
Thanks and I agree with you, but I am giving it my all. I just jumped into my first class with this material and I fear I may be to far behind. Thanks for the help

#### WBahn

Joined Mar 31, 2012
26,871
Thanks and I agree with you, but I am giving it my all. I just jumped into my first class with this material and I fear I may be to far behind. Thanks for the help
It's very possible that you are, indeed, too far behind. If that's the case, then you will likely be best served in the long run by taking a step back and taking (or retaking) the courses that lead up to this one. This material is foundational; even if you scrape by in this course, you are building a weak foundation and that will come back to haunt you.

#### shteii01

Joined Feb 19, 2010
4,644

#### LvW

Joined Jun 13, 2013
1,478
shteii01, you should better check the contents of a link before posting.

The given link defines a term "critical frequency" - however, obviously this is NOT the "critical" frequency ytiml1974 has mentioned in his post. (This can easily be seen by comparing the frequencies in the first post).

My recommendation to ytimk1974: Forget the link and follow the recommendation from WBahn.
And - yes, your assumption is correct: The frequency called "critical" seems to be the 3-dB corner frequency of both the open and the closed-loop gain, respectively.

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