AD8137: High offsert

Q

The specification of Vo,cm offset voltage is +/-28mV max. (Datasheet page 3);
My tested sample shows right values for Vo,dm, but Vo,cm is about 200mV; Is it
possible, that Vo,cm could be as high as 200mV? I think this is too much!

A

The main cause of unexpectedly high offset for our differential amplifiers is
imbalance (poor matching) of the Rf and RG resistors.
In the AD8137 datasheet this is mentioned in the section called Estimating DC
Errors on page 21 ; additional information is in the following section
Additional Impact of Mismatches in the Feedback Networks.
There will also be temperature related offset drift effects - see Figures 49
and 51 in the datasheet.