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

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Discussion Overview

The discussion revolves around calculating the voltage gain (Vo/Vi) of an op-amp circuit, specifically focusing on inverting and differential amplifier configurations. Participants are attempting to clarify the circuit setup and the application of relevant equations.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in starting the problem and seeks initial guidance.
  • Another participant points out that an attached file does not apply to the circuit in question and suggests redrawing the circuit for clarity.
  • A participant provides calculations for the inverting amplifier and differential amplifier, arriving at a voltage gain of Vo/Vi = 122.233.
  • There is confusion regarding the definitions of R1 and R2, with one participant asking for clarification on their roles in the equations.
  • Participants note inconsistencies in the application of the equations, particularly regarding the operations (multiplication vs. addition) applied to VX and VIN.
  • One participant asserts that their calculated result of Vo/Vi = 122.233 is correct.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the definitions of R1 and R2, and there is ongoing confusion regarding the application of the equations. The discussion remains unresolved regarding the correct interpretation of the circuit and the calculations involved.

Contextual Notes

There are unresolved definitions for R1 and R2, and participants have not clarified the assumptions behind the circuit configuration or the calculations. The discussion also highlights potential errors in the application of mathematical operations in the voltage gain equations.

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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