# Op amp analysis transfer function

Discussion in 'Homework Help' started by Jacl, Feb 15, 2013.

1. ### Jacl Thread Starter New Member

Feb 15, 2013
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I need a little help here. This is an ideal op amp. I need to find the transfer function Vi/Vo.

This is what I have so far (nodal analysis):

Then I'm not sure about the op amp gain , Vb = A * Vo?

I get confused when I try to proceed.

2. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,621
468
I think you really want to find the transfer function Vo/Vi, don't you?

Also, the opamp gain is Vo=Vb*A, not Vb=Vo*A

The two equations you have appear to be the KCL derived relationships at node a and node b.

You need another equation.

A = 1+R4/R3, so Vo=Vb*(1+R4/R3). This will serve as one more equation.

Now you just eliminate Va and Vb; do you know how to do that?

Jacl likes this.
3. ### Jacl Thread Starter New Member

Feb 15, 2013
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Yes, I meant Vo/Vi. Thanks for your help! I understand it now.

4. ### halfknot New Member

Apr 21, 2013
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Somewhat related question:

If I have a a 1st order op-amp low-pass filter circuit that also gives signal inversion: How do I perform an ideal op-amp analysis to give the voltage transfer function of the circuit?

5. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,621
468
Start a new thread, post a schematic, ask your question.

Show what progress you have already made in solving the problem.