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As mentioned by FvM, gain is a small signal parameter and, therefore, is independent on the bias point. Offset voltage influences only the bias point of the opamp - without touching the gain value.
But vice versa: The gain at f=0 largely influences the offset output voltage.
The opamp SMALL SIGNAL gain is "the ratio of the variation of the differential output voltage to the variation of the differential input voltage."
You can see it as
gain = ΔVout/ΔVin
More precisely the gain is the SLOPE of the opamp transfer characteristics at a specific point (usually the DC operating point).
As you can see from the circuit model, the offset just adds to the differential input voltage. Which means it have nothing to do with the SLOPE of the input/output transfer characteristics of the opamp. It just shifts this characteristics left or right.
From this you can conclude the following:
- Small signal Gain is unrelated to offset
- Offset seems to be a form of non-linearity in the opamp characteristics.
\]
That's right.
In my case, I provoked an offset (because I want it).
And I though that I could make an expression of the opamp gain depending on its offset.
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