cut off frequency

Discussion in 'Homework Help' started by jstrike21, Feb 18, 2010.

Sep 24, 2009
104
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I have a circuit with the transfer function: Vo/Vi=-R2/R1

How do I get the 3dB frequency from this?
Is it where 20log(Vo/Vi)=1/sqrt(2) ?

2. t_n_k AAC Fanatic!

Mar 6, 2009
5,448
790
The transfer coefficient for the relationship you give is constant for all frequencies - there is is effectively no cut-off frequency.

Sep 24, 2009
104
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That is what I thought but I looked at the question again and it gave me GB=2MHz
so I did 2pi(MHz)=(R2/R1)w

4. hgmjr Retired Moderator

Jan 28, 2005
9,030
218
Can you provide a schematic so that we may see what it looks like?

hgmjr

Sep 24, 2009
104
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forgot to say its an op amp circuit

6. beenthere Retired Moderator

Apr 20, 2004
15,815
293
The limiting factor is the slew rate of the op amp.

7. steveb Senior Member

Jul 3, 2008
2,433
469
Slew rate can limit the response for large signals. But, for small signals it is the gain bandwidth which limits the response.

The key thing which is apparent here is that insufficient information has been given so far. We need to know more about the properties of the opamp and whether the analysis is for large signals or a small signal approximation.

I would guess that the problem has given a gain bandwidth, or an open loop gain with a pole location, and is asking about small signal gain.