# Voltage gain Vo/Vi

1. Mar 20, 2016

### gazp1988

1. The problem statement, all variables and given/known data
Determine the voltage gain Vo/Vi of the op-amp circuit

2. Relevant equations
inverting amplifer
vout=-(Rf/Rin) x vin

differential amplifer
vout= (R2/R1) x (vo - vin)

3. The attempt at a solution
im really struggling to even get started with this one sorry for the limited information i just need a starting block.

#### Attached Files:

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Last edited by a moderator: Mar 21, 2016
2. Mar 21, 2016

### Tom.G

The file you attached is not applicable to the circuit in your post. Notice that in the attached file there is a path from output to the "+" input of the same opamp. That configuration is not in your posted circuit.

Try redrawing your circuit by moving the lower opamp upward and to the left of the upper opamp, and make it face in the same direction. That should help in seeing the overall function. If you're still having trouble, start by considering the two opamp circuits individually.

Where/what are R2, R1?

3. Mar 21, 2016

### gazp1988

sorry about the attached file i dont know why it did that, it has nothing to do with my circuit.

this is what i have so far.

inverting amplifier

vout= -(RF/RIN) X VIN
Vout = -(68/12) x Vin
Vout = -5.667Vin

Differential amplifier
vout = -(R2/R1) x (VX x VIN)
Vout = -(220/12) x (VX x VIN)
Vout = -18.334 x ((-5.667Vin) - Vin)
Vout = -18.334 x (-6.667Vin)
vo/vi = 122.233

4. Mar 21, 2016

### Tom.G

VX and VIN are Multipied here...
WHY?

R1 & R2 are still undefined.

5. Mar 21, 2016

### Eucliddo

Where/what are R2, R1?[/QUOTE]

R2 in the formula is the feedback resistor, R1 the series one.

6. Mar 22, 2016

### LvW

This result is correct.