MOSFET drain-to-substrate and source-to-substrate capacitances in Multisim

[dbeams]

I am modeling MOSFETs using the Level 1 model parameters provided by Sedra and Smith, 7th Edition, Table B.3.  Among the model parameters are AS (source area), PS (source perimeter), AD (drain area), and PD (drain perimeter).  These parameters are needed to compute drain-to-substrate and source-to-substrate capacitances.  However, the Multisim model does not recognize them.  The Multisim model does recognize CJ (junction bottom-plate capacitance, F/m^2), MJ (bottom junction grading coefficient), CJSW (junction sidewall capacitance, F/m) and MJSW (sidewall junction grading coefficient).  So when I run my simulations, I get a warning that the parameters AD, PD, AS, and PS are unrecognized and the source/drain-to-substrate capacitances are zero.  Does anyone have ideas how I could get Multisim to compute the source-to-substrate and drain-to-substrate capacitances?

[David22JRA]

Hello dbeams

Thanks for posting your concern here. In my research I found a document that explain the syntax you should use so, I would like you use it. See the link below

https://www.ni.com/en/shop/electronic-test-instrumentation/application-software-for-electronic-test-... (scroll down in Mosfet)

Also, feel free to attach a screenshot showing the syntax you are using.

Regards.

[dbeams]

The model is attached as is a snip from the Multisim reference to which you linked.  The Multisim reference includes parameters AD, AS, PD, and PS.  Also attached is a copy of the warning generated by Multisim.  When I check the audit trail, the drain-to-substrate capacitance seems to be zero.  Copy attached.  So I am baffled...the reference manual says these (PS, PD, AS, and AD) are legitimate parameters, but Multisim says no, and the capacitances associated with the source-substrate and drain-substrate junctions are zero.  So...what am I missing? 

[dbeams]

Forgot to include the Multisim warning message indicating that PS, PD, AS, and AD are not recognized.

[David22JRA]

Hello dbeams

What I have noticed is that the syntax is pretty differente as the document shows regarding with the syntax you used.

Syntax	Mname ND NG NS NB MNAME <L=VAL> <W=VAL> <AD=VAL> <AS=VAL> <PD=VAL> <PS=VAL> <NRD=VAL> <NRS=VAL> <OFF> <IC=VDS, VGS, VBS> <TEMP=T>
Example	M31 2 17 6 10 Mname L=5U W=2U

Also, I will research more to see what we can do.

Regards

[dbeams]

I don't see that my syntax is really much different from that specified by the reference manual.  And the reference manual lists optional parameters <PD>=VAL, <PS>=VAL, <AD>=VAL, and <AS>=VAL which are the ones that generate warnings from Multisim.  I don't think it is because the syntax in specifying these values is wrong...for example, in my model, I have PS=67.5u (which means that the perimeter of the source is 67.5um).  I don't see a problem there.

I should mention that I have used these parameters in PSpice models without problem.  

It may be helpful if I mentioned that I was using Multisim 12.  The latest version I have available on another machine is Multisim 13.  I could try that and see if the same problem occurs.  

[David22JRA]

Hello dbeams

That sounds good, let me know if something changes.

Regards