Electronic – Op Amp Input Offset Voltage vs Common Mode Voltage

amplifiercommon-modeinput-offset-voltageoperational-amplifier

I would like to use an op amp AD8618 for a design, and need the input offset voltage to be low. For this op amp it seems fine with maximum of 65uV, but looking at the charts on page 6 etc, it seems to indicate that the input offset voltage in fact changes depending on the common mode voltage (at the inputs?) to much higher than that. (https://www.analog.com/media/en/technical-documentation/data-sheets/AD8615_8616_8618.pdf)

I intend to bias the amp at 2.5V, which could mean very poor results!? Is this a characteristic of all op amps, could someone explain to me or provide me a resource on this phenomenon?

Best Answer

This is a common characteristic of rail-to-rail input op-amps. There are really two front ends and there is a transition between them at some common-mode voltage. R-R output is irrelevant.

If you care about Vos to that extent, you can choose another type of op-amp. Maybe a chopper type, but they have other subtle (and not so subtle) imperfections.