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

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SUMMARY

The voltage gain Vo/Vi of the op-amp circuit is calculated using the formulas for inverting and differential amplifiers. The inverting amplifier formula is given by Vout = -(Rf/Rin) x Vin, resulting in Vout = -5.667Vin with Rf = 68Ω and Rin = 12Ω. The differential amplifier formula yields Vo/Vi = 122.233, where R2 = 220Ω and R1 = 12Ω. The calculations confirm that the defined values for R1 and R2 are crucial for determining the overall voltage gain.

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gazp1988
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Homework Statement


Determine the voltage gain Vo/Vi of the op-amp circuit
upload_2016-3-20_21-57-54.png

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.
 

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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.

gazp1988 said:
differential amplifer
vout= (R2/R1) x (vo - vin)

Where/what are R2, R1?
 
sorry about the attached file i don't know why it did that, it has nothing to do with my circuit.o_O

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
 
VX and VIN are Multipied here...
gazp1988 said:
Vout = -(220/12) x (VX x VIN)
...but Added here.
gazp1988 said:
Vout = -18.334 x ((-5.667Vin) - Vin)
WHY?

R1 & R2 are still undefined.
 
Where/what are R2, R1?[/QUOTE]

R2 in the formula is the feedback resistor, R1 the series one.
 
gazp1988 said:
sorry about the attached file i don't know why it did that, it has nothing to do with my circuit.o_O

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

This result is correct.
 

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