Need help with Monte Carlo Analysis

[dsk635]

Hi,

I am using Orcad Capture for simulating my design. I have an opamp based design. I need to find out how the offset voltage of the opamp varies when there is variation in the Vth of the other transistors. Basically, I need to use a distribution, say Gaussian, for the Vth variation of all transistors in the design except for one of the input transistors of diff. amp. Each run of the analysis will then do a vth variation (model parameter variation) of this input MOS and show how the output of the opamp varies as vth of other transistors vary. I hope I have made my problem clear.

I'd appreciate any tips/help in solving this.
Thanks!
-D.

 

[lovseed]

you need to define a parameter say vth_vary, and add this vth_vary to the vth0 in the model card, say vth0="xxxxxx + vth_vary" and then specify a guassian distribution for vth_vary in monte carlo sweep.

You need to define another model name for the only transistor which you do not want to change vth. This model will not have vth_vary in its vth0 parameter.

Hope this solves your problem.

 

[dsk635]

Hi,

Thanks for the help. I am facing another problem - Orcad Capture is not allowing me to use Monte Carlo analysis where each run is a DC sweep of a model parameter

Is there any way I can go around this limitaion?

Thanks,
-D

 

[lovseed]

i have not tried, but this kind of tools should have the ability.

Try using HSPICE? I think they are almost the same.
Or you can change DC analysis to transient analysis.
Dive into the manual.