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.

 

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?

 

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?

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

 

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?

 

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