My understanding is that  a Device L/W mismatch Monte Carlo  analysis in spectre includes all the active devices in the circuit on which the simulation is run.  My issue , that  I was hoping for a bit of guidance on, is that my circuit includes a model of a SPAD (Single Photon Avalnche Diode) which I designed separately. It is included into the circuit as a symbol. I do not want the active devices within the SPAD symbol to be involved in the MC analysis I am running on the circuit. In other words, I need the Lenght and Width vary statements in my statistic block to leave the L and W of the active devices within the SPAD model alone and only act on the active devices outside the symbol. I do not have that option of running the simulation on the circuit without including the SPAD Model, as my results would be meaningless in such event. Is there way a to make this distinction in spectre... Am I right in assuming that the devices within my SPAD (Model) symbol will also  be included in the MC analysis .. Thank you

hmmm .. That's interesting. Let me see if I am understanding you right. l and w  are default device parameters. In order to perform a MC mismatch analysis I have to include a Statistics block and within it a vary statement in the device model file. The Parameter of the vary statement have to be  valid parameters of the device.. i.e l and w. This will then vary statistically the' l' and ' w' of all the devices within the circuit under simulation. I was asking to see if there was a way for me to exclude certain devices in the circuit from the EFFECT of the 'vary' statements i have included in the model file... bit I think what you are suggesting is for me to edit the 'l' and 'w' parameters definition and define them in terms of another variable ... say 'l_vary'..somethign like this : ( l = l*iPar(l_vary)  ) Butr to only do this for the devices I need included in the mismatch analysis. Then I can change the vary statement in the Model file to ( vary l_vary dist=gauss std= ......) instead of ( vary l dist ... ). Am i understanding you correctly? .. oh , and BTW - Thank you for your response.