Calculating Voltage Gain Vo/Vi of an Op-Amp Circuit

[gazp1988]

Homework Statement

Determine the voltage gain Vo/Vi of the op-amp circuit

Homework Equations

inverting amplifer
vout=-(Rf/Rin) x vin

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

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.

 

[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.

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

Where/what are R2, R1?

 

[gazp1988]

sorry about the attached file i don't 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

 

[Tom.G]

VX and VIN are Multipied here...

Vout = -(220/12) x (VX x VIN)

...but Added here.

Vout = -18.334 x ((-5.667Vin) - Vin)

WHY?

R1 & R2 are still undefined.

 

[Eucliddo]

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

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

 

[LvW]

sorry about the attached file i don't know why it did that, it has nothing to do with my circuit.

this is what i have so far.
vo/vi = 122.233

This result is correct.