ericgibbs

Hi Frosty,
Not wishing to add to the confusion,
I would read the application datasheets for OPA's and check the accuracy of using 'nulling' in the above statement.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
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Roff

In an inverting amp, what you say is true.
In a noninverting amp,
EDIT: Oops! I had this equation wrong the first time.
Av = (Rf+Rs)/Rs
The current injection resistor is part of Rs. It is therefore in the gain equation. In addition, varying the pot causes the value of that resistor to change slightly.

EDIT: Here's another way of looking at it. The inverting input is not virtual ground, it is virtual input signal. Therefore, signal-related current through the current injection resistor (Ri) will be Vin/Ri.

__________________
Ron