I downloaded the spice model for AD8676 and tried to simulate the noise in LTspice.
My circuit is really simple (see attached pdf).
The opamp is connected as a unity gain buffer. The only resistor is an Rs from the positive input to ground.
I am using +/-15V supplies (I also checked with +/-5V supplies and get same results).
I then swept the Rs value from 1 to 1G and plotted V(onoise) at 1kHz.
From that I find:
The datasheet says
Vn = 2.8nV/rHz
In = 300fA/rHz
So the simulated voltage noise seems to be ~10x too high and current noise is 15x too low.
Am I doing something wrong or is there a problem with the model for AD8676?
Thank you for your question. I have tried AD8676 noise simulation in Multisim and produced the same results as yours. I believe that the AD8676 noise model has an issue and that I will forward this to the group that modeled the AD8676 SPICE so that it will be corrected.