# Dual op-amp output voltage as function of source

1. Mar 5, 2014

### Maylis

1. The problem statement, all variables and given/known data
Find Vo as a function of Vs

2. Relevant equations

3. The attempt at a solution
My thought process so far is to do KCL and find Vo as a function of Vn2, then Vn2 as a function of Vo1, then Vo1 and Vo as a function of Vn1, then Vn1 as a function of Vs, finally giving me Vo as a function of Vs. This seems extraordinarily difficult to do all those substitutions, but I see nothing else as of this moment

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2. Mar 5, 2014

### Staff: Mentor

Keep in mind the properties of op-amp circuits where negative feedback is provided. How are the potentials on the input terminals related?

I'd suggest beginning with the output stage and determine what Vo is in terms of Vo1. Then KCL at the Vn1 node.

3. Mar 5, 2014

### donpacino

do a kcl at all non driven and non ground nodes.
in other words, do a kcl at the negative nodes of each op-amp.
then solve for the answer

4. Mar 5, 2014

### Maylis

Alright following your collected guidance, my friend and I solved it and got the same answer. Thank you! I did not set the voltage at the inputs to zero, no wonder it was so complicated.

5. Mar 5, 2014

6. Mar 5, 2014

### Maylis

Vo = Vs (Rf1*Rf2*Rf3)/(Rs1(Rs2*Rf3-Rf2*Rf1))

7. Mar 6, 2014