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Virtual short?

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Electronman

New Member
Hello guys,

I have a question regarding to Op-Amps.

I have read somewhere that there is a zero voltage deference between op-amp's inputs at some situation, the guy who wrote the paper called it virtual short connection.
What's that really and why it does happen? Does it exist for non inverting op-amps too? If two inputs (inverting and non inverting pins) have the same voltage so how does input signal affects the op-amps while the other pin is grounded?
I do not that the negative feedback lowers the input signal to several micro volts but it means that there is a small voltage deference between the 2 inputs (inverting and non inverting).
Besides if we consider the voltage deference of '+' and '-' pins in zero volts then there is not any deferential voltage at those pins to go into op-amp for amplifying?

Thanks for any help.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
Look thru this pdf, explains it in basic terms.:)

refer page 24.
 

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confounded

New Member
I have read about 'virtual ground' is this what you mean?
You can see the op amp as changing its output in order to keep voltage difference between inputs zero.
Therefore if one input is connected to ground the op amp will make the other input ground as long as its output is not saturated.

You dont get virtual ground for non inverting amps as the inverting input is not at ground. The op amp does try to keep both inputs the same voltage however.

If you see a schematic for an op amp it has a differential amplifier as input this is why an op amp does this.
 
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