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What is amplified in inverting opamp ?

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yemi11

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All sources writes the kirchoffs current law for the node between Rf and Ri (in picture) and and writes a relation between equations for opamp.

invOpamp.jpg
that results in -Rf/Ri

But what actually opamp amplifies and multiply with 200000 or whatever ?

if Noninverting input is zero. Than,

A*(0-Vinverting)=Voutput (A, open loop gain..)

What is Vinterting ?
 
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LvW

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The voltage at the inv. node Vn can be calculated using all the classical formulas:

Superposition:
* Vn1=f(Vin) for Vout=0
* Vn2=f(Vout) for Vin=0
* Vn=Vn1+Vn2=-Vout/Ao
 

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