What is the Voltage Gain of Vo/Vi in an Op Amp Circuit?

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Discussion Overview

The discussion centers around calculating the voltage gain (Vo/Vi) in an operational amplifier (op amp) circuit, specifically focusing on inverting and differential configurations. Participants are sharing their attempts at solving a homework problem related to this topic.

Discussion Character

  • Homework-related

Main Points Raised

  • One participant presents their calculations for the voltage gain in an inverting op amp configuration, arriving at a value of 121.878.
  • Another participant confirms that the result looks good but suggests adding comments to clarify the derivation steps, noting some confusion with the variable symbols.
  • A third participant mentions they obtained a slightly different result of 122.22, indicating that while their answer is not exact, it is close to the first participant's result and suggests improving clarity in the solution.
  • A later reply questions whether the similarity in problems is coincidental.

Areas of Agreement / Disagreement

Participants express differing numerical results for the voltage gain, indicating that there is no consensus on the exact value. However, there is general agreement that the calculations are in the same ballpark, and suggestions for clarity in presentation are made.

Contextual Notes

Some participants note potential confusion regarding the use of variable symbols (R1 and R2) taking on different values, which may affect understanding of the derivations.

StripesUK
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Homework Statement


Find the voltage gain of Vo/Vi. I'm pretty confident I have this down now, but I'd be greatful if someone could confirm I have this sussed.

Homework Equations


For the inverting op amp:
Vo= \frac{-R2}{R1}*Vi
For the differential op amp:
Vo= \frac{-R2}{R1}(V--V+)

The Attempt at a Solution


Vx= \frac{-R2}{R1}*Vi
Vx= \frac{-68}{12}*Vi=-5.667Vi

Vo= \frac{-R2}{R1}(Vx-Vi)
Vo= \frac{-220}{12}((-5.667Vi)-Vi)
Vo= \frac-18.3(-6.66Vi)=121.878Vi

\frac{Vo}{Vi}=121.878
 

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The result looks good.

You might want to sprinkle a few comments around in your derivations so that it's obvious what your steps are accomplishing. It was a bit puzzling at first to see the same symbols, R1 and R2, take on different values with no apparent reason.
 
I've read this exact problem this morning and got 122.22. It may not be as exact as your answer but it's just the same. Just make your solution clearer to avoid confusion.
 
Coincidence that this is the same exercise ?
 

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