AnsweredAssumed Answered

AD628 common mode offset on the output

Question asked by RAURIOL on Jun 13, 2018
Latest reply on Jun 18, 2018 by RAURIOL

Hello,

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 ?

 

Thank you

Robin

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