Opamps have very high differential gain when their outputs are not saturated either positive or negative. So it takes a very small differential voltage times all that gain to keep the output voltage not saturated fully positive or negative.
Therefore, the simplifying assumption is that if the opamp is in the linear (not saturated output) range, the differential input voltage must be approximately zero.
I don't understand a thing. Why vid (volt inputs differential) is null, only when op.amp. works in linear zone? Thanks in advance.
Because the ideal opamp has infinite gain, and anything multiplied by infinity is infinity. In engineering we tend to use infinity when we mean a very large number, sometimes even as big as 255.
Paul Burke
Thanks in advance.
If the vid was zero the opamp would be operating in the "linear zone"
The only reason it is not zero is if the opamp can not drive the output far enough to make it zero
Because the output voltage is almost infinite times the input voltage differential.
Rene
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