Electronic Instrument Amplifier

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Discussion Overview

The discussion revolves around the analysis and design of an electronic instrument amplifier circuit, specifically focusing on the configuration and functionality of operational amplifiers (op-amps) within the circuit. Participants are examining the roles of different op-amps, their configurations, and the resulting output equations based on resistor values.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant identifies OA2 as a non-inverting amplifier and OA1 as a voltage follower, questioning whether the final op-amp OA3 acts as a summarizing amplifier with two inputs into the negative terminal and a feedback resistor R5.
  • Another participant agrees with the analysis but corrects the terminology, stating that OA3 is a "summing" amplifier rather than a "summarizing" amplifier.
  • A participant reports an output equation of V_out = -20(V1) - 1.961(V2) and questions whether this is correct, noting that the gain for V2 should also be around 20.
  • There is a suggestion that to achieve a new desired output of V_out = 25(V1) - 10(V2), changing the resistors may not be sufficient, and that OA2 might need to be an inverting op-amp to switch the sign of V1.
  • Another participant presents their calculations for V_out and questions the accuracy of their results, indicating that the ratio R5/R4 does not equal 1.96, suggesting a potential error in their analysis.

Areas of Agreement / Disagreement

Participants generally agree on the roles of the op-amps in the circuit, but there are differing views on the correctness of the output equations and the necessary modifications to achieve the desired output. The discussion remains unresolved regarding the accuracy of the calculations and the implications for circuit design.

Contextual Notes

There are unresolved questions about the specific resistor values and their impact on the output, as well as the assumptions made in the calculations. The terminology used for the op-amps may also lead to confusion.

foobag
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Need some help guys

https://www.physicsforums.com/attachment.php?attachmentid=32237&d=1297816285

I began to analyze it and I got to this:

OA2 is a non inverting amplifer
OA1 is a voltage follower

thus:

V1(1+ (R1/R2) is the input for R3 into the final op-amp OA3 which is an inverting op-amp. And V2 is the second input that goes through R4 into the op-amp OA3.

Could someone please verify my logic, and tell me whether this is a summarizing op-amp in the end with 2 inputs into the negative terminal, with feedback resistor R5?

Thanks!
 
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foobag said:
Need some help guys

https://www.physicsforums.com/attachment.php?attachmentid=32237&d=1297816285

I began to analyze it and I got to this:

OA2 is a non inverting amplifer
OA1 is a voltage follower

thus:

V1(1+ (R1/R2) is the input for R3 into the final op-amp OA3 which is an inverting op-amp. And V2 is the second input that goes through R4 into the op-amp OA3.

Could someone please verify my logic, and tell me whether this is a summarizing op-amp in the end with 2 inputs into the negative terminal, with feedback resistor R5?

Thanks!

Could you please re-post the attachment? Something happened with it. (not your fault, I don't think)
 
Last edited by a moderator:
thanks for your input

i got a funny output: V_out = -20(V1) - 1.961(V2)

the 2nd part of the question asks to design a new circuit with Vout = 25(V1) - 10(V2), so aside from changing the resistors would I have to change OA2 into an inverting op amp itself so that it potentially switches the sign of V1 from negative to positive?

thanks!
 
foobag said:
thanks for your input

i got a funny output: V_out = -20(V1) - 1.961(V2)

That doesn't look right. The V2 gain should be about 20 as well, I think. Can you post your work?

the 2nd part of the question asks to design a new circuit with Vout = 25(V1) - 10(V2), so aside from changing the resistors would I have to change OA2 into an inverting op amp itself so that it potentially switches the sign of V1 from negative to positive?

thanks!

Yes, you would invert the first gain stage for V1.
 
i did v1(1+(r1/r2))/r3 + v2/r4 = -Vout/R5

so vout = -(r5/r3)V1(1+(r1/r2)) - (r5/r4)v2

pluggin in resistor values i got

vout = -20v1 - 1.961v2

is this wrong?
 
foobag said:
i did v1(1+(r1/r2))/r3 + v2/r4 = -Vout/R5

so vout = -(r5/r3)V1(1+(r1/r2)) - (r5/r4)v2

pluggin in resistor values i got

vout = -20v1 - 1.961v2

is this wrong?

R5/R4 is not equal to 1.96...
 

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