I want to simulate an input offset voltage in a spice simulation.

I have the following circuit...


If I add 1.25mV to the non-inverting terminal, is this the same as adding an input offset?

 

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If I add 1.25mV to the non-inverting terminal, is this the same as adding an input offset?

Yes.
It can be added to either (but only one) terminal.
But note that many spice op amp models already include an input offset.
Run the simulation for the op amp as a non-inverting follower with the input grounded and see what output offset is indicated.

 

Thanks much.