Thanks, paul. dvthn(p) are used for process corners. But I think it doesn't matter to use it for mismatch too. Anyway, I've tried using another parameter like vthmis and changing the equation for vth0 to be sth like
vth0=vthmis*(0.4xxx+dvthn).
But still no use.
By the way, the simulation result is the same from run to run if I choose "Mismatch Only" in monte carlo GUI window.
[quote author=Paul link=1074804759/0#1 date=1074887862]Stephen,
the first thing you should not forget is that matching for MOS devices is size dependent, which is not the case in your file. Have a look at EVI's example in
http://www.designers-guide.com/Forum/?board=circuit;action=display;num=106670695...Further more, I don't know your model file, but I would guess dvthn (and p) are used to calculate the corner values for VTH, so you should use a different parameter name for your mismatch simulations (again see EVI's example).
Regarding your problem, I don't know very well the detailed MC calculations performed by Spectre, but as you don't use subcircuits to interface the devices with the models, the simulator may calculate once per run the mismatch and apply the same mismatch to both devices. Does your simulation give different operating points from one run to the next?
Maybe EVI or BSIM4, doing these simulations with Spectre, can help here?
Paul [/quote]