Dear Community,
I'm using a submicron PDK from a well known foundry and I've noticed the duplication of almost all of the devices in "DeviceName
_mis" variant to allow mismatch simulation when running MC mismatch.
I was a little bit surprised by this methodology since I've used many other PDKs from other companies and that's the first time I'm seeing this.
Well, this was really anoying me and some of the designers I'm working with because you need to suplicate every single schematic sheet ...
I went through the Spectre model file and I managed to write a parser that makes a slightly different Model file with Sections ordered differently. This allowed me to use a single schematic and just switch bck and forth between the sections when including the model file. So the problem of duplicating the schematics is resolved so far but ... I'm still wondering why the models are duplicated ?????
I made a diff between the "NmosX" subckt/Bsim_model and the "NmosX_mis" and the difference stands only for the mismatch-impacted parameters (VT, Tox, ...). But this difference appears only in statistical simulation since the mean/DC value of the Delta_for_Mismatch is ZERO. In other words, if you simulate both "NmosX_mis" and "NmosX" in a non-MC (let say a DC OP), you will get exactly the same results. I dumped the Spectre DC info results into ASCII files (input.info.models, input.info.output ...) and compared them all : NO DIFFERENCE.
I've done the same job for the passives and all devices duplicated into "_mis" variant. Same results in DC.
My conclusion at this stage is that the models are just redundant ...
Well, I think the guys who made this from this company are clever enough to avoid duplicating data, that's why I believe there is a reason behind but I don't see it actually ...
Any comment on this is more than welcome !
Thanks in advance.
Riad.