How can I add custom mosfet models?

[svenboulanger]

Hi!

Is it possible to add my own LEVEL for mosfet models, and how would I do that? I would like to tie the BSIM3-6 models into Spice#.Parser and read foundry models.

Yours sincerely,
Sven

[marcin-golebiowski]

Take a look at CustomMosfetModelTest class and When_CustomMosfetModel_Used_NoExceptions test.

[svenboulanger]

Hi, thanks for the reply! I can see how I can add a custom mosfet level.

Another piece of SPICE syntax that I see is the lmin, lmax, wmin and wmax parameters.

.model nmos_mod.1 nmos (lmin=65n lmax=180n wmin=100n wmax=1u ...)
.model nmos_mod.2 nmos (lmin=180n lmax=350n wmin=100n wmax=1u ...)
...

* This automatically selects nmos_mod.2 based on the width and length parameters
Mnmos drain gate source bulk nmos_mod w=0.5u l=200n

For example, this occurs in the BSIM3v3 model (ngSpice version in section A.9), and it is used by the CMOS foundry PDKs that I'm trying to parse. Is this feature supported?

Yours sincerely,
Sven

[marcin-golebiowski]

Parsing parameters of Mosfet model is supported by default. However you need to use Mosfet model that supports lmin, lmax, wmin and wmax parameters

https://github.com/SpiceSharp/SpiceSharp/blob/master/SpiceSharp/Components/Semiconductors/Mosfets/Level3/ModelParameters.cs
seems to not support it.

[svenboulanger]

I think we may have reached a limitation. If I read this correctly, I think you're saying that it should be supported by the Spice# core library (or at least the model/instance code), but I fear that there currently is not a good way to deal with this feature. I can identify a few "problems":

• Unused models don't have to be loaded if there are no instances pointing to them. Spice# core does not know how to "cut out" these models.
• Instances refer to a model by name, but in this case it would point to a "set" of models of which one is chosen dynamically. This gets tricky for things like sweeping the width of a transistor, which might cause the instance to move from one model to another.

What's your thoughts?

[svenboulanger]

I have been thinking about what you said. I think it may be possible without the need to change the Spice# core library. I could make a model that contains one or more models, and the mosfet instance should then request the correct one from the aggregate model. I'll start with implementing that and then come back to see what we can do in the parser. Thanks!