i'm using an AD628 on my project.
I'd like to measure a 0-30mV signal with a common mode voltage between 0-5V.
Here is the circuit :
The Gain of this circuit is 10 (First stage gain: 0.1, Second stage gain: 100).
According to the datasheet, the error induced by the input common mode on the output is as follow:
In my case that means : Voffset = 0.1 x 3 x 100 / (10^3.75) = 5mV
and so an error of 1.7% on the output.
But the reality is worst : for a 3V common mode i find a 14mV offset error on the output...
Does anybody have a solution to my problem ?
What am I missing ?