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Question about Finding Gain Parameters

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frozone45

New Member
Hi everyone, I had a question about finding gain parameters. The question is part "c" in the attached "Gain Parameters Problem Picture.pdf" file. The correct answers to the problem are 18.86 [A/A] for Aisc and 9.428 [V/V] for Avo. My work for the problem is in the attached "Gain Parameters Problem Work Part 1.pdf" and "Gain Parameters Problem Work Part 2.pdf" files.

I don't understand why there is only one correct value for Aisc and one correct value for Avo in this problem, since there are two different values for "vi", the voltage across resistor "Riv". I used these two different values of "vi", which were "0.14 [V]" and "-0.14 [V]", to find two different values each, for Aisc and Avo. The values I got for Aisc were -18.86 [A/A] and 18.86 [A/A]. The values I got for Avo were -9.428 [V/V] and 9.428 [V/V]. I would appreciate any help in understanding why there is only one correct value for Aisc and Avo.
 

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michiel

New Member
the voltage vi you calculated is a rms voltage
this means the dc equivalent of the ac voltage is the value of vi
the peak voltage would be vi*square root(2)
this signal goes from +vi*sqrt(2) to -vi*sqrt(2)
if vi were negative the limits of the ac signal wouldnt change only the phase which is not important since
you are only concerned with the amplification
 

Ratchit

Well-Known Member
Hi everyone, I had a question about finding gain parameters. The question is part "c" in the attached "Gain Parameters Problem Picture.pdf" file. The correct answers to the problem are 18.86 [A/A] for Aisc and 9.428 [V/V] for Avo. My work for the problem is in the attached "Gain Parameters Problem Work Part 1.pdf" and "Gain Parameters Problem Work Part 2.pdf" files.

I don't understand why there is only one correct value for Aisc and one correct value for Avo in this problem, since there are two different values for "vi", the voltage across resistor "Riv". I used these two different values of "vi", which were "0.14 [V]" and "-0.14 [V]", to find two different values each, for Aisc and Avo. The values I got for Aisc were -18.86 [A/A] and 18.86 [A/A]. The values I got for Avo were -9.428 [V/V] and 9.428 [V/V]. I would appreciate any help in understanding why there is only one correct value for Aisc and Avo.
Why do you say there are two different voltages across Riv? You are given the current and the power dissipated in the resistor, so there can only be one voltage across Riv.

Ratch
 

MrAl

Well-Known Member
Most Helpful Member
Hello,

Sometimes the power is signed but because this is a resistor we consider it to be non signed or always positive. That gives rise to the fact that the current can be positive or negative and we still get that 1mw. However, in this problem the current is also given and assuming conventional current flow that means the current flows as the arrow shows in the input source. That means the current can only flow one way, not both, meaning there should be only one answer for the current in the target resistor, and that means only one value of gain.

Sometimes the gain is given as unsigned too, but we dont have to resort to that in this problem because as above the current can only flow one way anyway.
 
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