how to determine the subthreshold process paramter?

Not sure where that equation comes from - you need to remember that any such equation may only reflect a specific model, and most modern transistor models are rather more complex than this (although it doesn't look like any basic transistor models either to me, but it may just be how it's written).

I could see that many of the "Philips" (now NXP) models (e.g. MOS11, MOS902 etc) have a parameter for subthreshold slope (this is a model parameter, called "mo" or "mor"), but there doesn't seem to be anything like that for bsim3v3, bsim4. So I suspect the model formulation doesn't have any similar parameter and it's not something the models compute and spit out either (I've not found any requests for this as an output or operating point parameter).

So given that you didn't say which model you're using, or which simulator you're using, or which version of the tools you're using, I rather doubt this can be answered. However, even knowing that, it doesn't look to me as if the equation you've described matches any of the models (from a very quick scan through the model documentation, which is in cdnshelp) in Spectre.

Regards,

Andrew.

Hi, I am using Cadence Virtuoso ADE L to simulate my circuit and I want to figure out the subthreshold factor. Can you help me out how to do so?

Arefinn said:

Can you help me out how to do so?

Not unless you both read the thread here (especially the last sentence in my reply to which you posted your question) and can provide a lot more information. What is this "subthreshold factor" you refer to? Which simulator and device models are you using? Which version of the tools are you using? Please provide a reference for any equation you might mention.



and I am using the kit GPDK090

Cadence (R) Virtuoso (R) Spectre (R) Circuit Simulator
Version 13.1.1.117.isr8 64bit -- 19 Jun 2014

You still didn't give a reference for those equations - just an image. In what text are they published? They don't look that familiar to me, and certainly don't match the bsim3v3 model equations used in GPDK090.  Presumably the reference [13] gives some more detail on this sub-threshold slope factor?

Unfortunately most of the relevant text books I have on this are stranded in the office, so I'm having to go on memory, a bit of googling, and looking in the Spectre Circuit Simulator Components and Device Models Reference manual.

Andrew.

The reference is Wang, A., Calhoun, B. H., & Chandrakasan, A. P. (2006). Sub-threshold design for ultra low-power systems. New York: Springer.

https://link.springer.com/content/pdf/10.1007%2F978-0-387-34501-7.pdf

The reference is Wang, A., Calhoun, B. H., & Chandrakasan, A. P. (2006). Sub-threshold design for ultra low-power systems. New York: Springer.

https://link.springer.com/content/pdf/10.1007%2F978-0-387-34501-7.pdf

Given that key authors in chapters of that book (I'm not familiar with it, and don't have access to it) are Christian Enz and Eric Vittoz, and it also talks about the EKV model (these two are the E and V in EKV), I would have expected that maybe this equation shows up in the documentation for the EKV or EKV3 model in Spectre. It doesn't. So I don't think I can help you - you'd be trying to fit one equation against another - and given that gpdk090 uses bsim3v3 (which is a totally different approach to compact MOS modelling than EKV), it's going to be difficult.

Andrew.

So you are saying it is not possible to plot or extract subthreshold slope factor n using this simulator? I would also like to add that this n is n = 1 + Cdep/Cox, hence is it possible to extract depletion layer and gate-oxide capacitancels repectively from this version of simulator? if so how?

As I said in the earlier answer (before the one you replied to) you are trying to use some model equation of how a transistor works, and trying to fill in parameters of that based on a completely different model that was used in simulation. It's a common mistake that people use textbook equations which might have been valid 30 years ago and assume you can get exact results in modern (or even not so modern) technologies. This is not something to do with "this version of the simulator" - it's the fact that the device equations used in the models you are referring to do not use the equations you've quoted. You might be able to work out how to fit one set of (not particularly commonly used) equations onto the equations actually simulated, and extract the numbers you're looking for, but this is a slightly odd thing to do...

Since this subthreshold slope factor is not part of the device models used, there's nothing in the simulator to output it. I cannot find it used in any of the models (other than the Philips/NXP models I mentioned before, and even then I'm not sure it means the same thing).

Other than this question being asked here (twice) - presumably the earlier question came about from the same book - I've not found anyone asking this question anywhere. I'd be surprised if any simulator directly outputs this value.

Andrew.