David,
First more information on what simulated parameter or phenomena
doesn't match simulation measurement would be useful: noise,
distortion, ...
While I haven't tested this or looked at this in detail yet, but my
first reaction is that wouldn't this have the same issues as a passive
mixer? That is, if you are using a non-surface potential model then
there will be issues with models characteristics around 0 Volts.
Next if the resistance is 10e12, then you might need to set gmin
to a different value so it does not effect dc operating point calculations
and potentially small signal simulation results.
Finally, maybe I need to read the paper
but how does a device
in cutoff act as a feedback component and contribute noise?
Sheldon