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15th June 2013, 12:28 PM  #1 
diyAudio Member

Using Excel "Solver" for MOSFET SPICE params
Motivated by Pierre Touzelet's 2007 AX article for deriving Triode params with Microsoft Excel, I made a video showing how to use "Graph Grabber" and "Solver" to create basic, level 1 spice params for MOSFETs:
https://www.youtube.com/watch?v=2vh1RbBJa0 The equations in the columns: Id(sat) = (KP/2) * ((Vgsvt)^2)*(1+Lambda*Vds) where KP is mu * Cox * (W/L) I figger "saturation" to be 90% of the current yielded at the maximum Vds for each set of Vgs curves  and test for this. Unsaturated data is thus nulled so that no error term is calculated. Pierre minimized "sum of the squared errors" for triodes. In the case of MOSFETs the saturation currents differ by orders of magnitude so "goodness of fit", "maximizing Rsquareds" were calculated. Rather than simply letting "Solver" do its thing, you might want to manually iterate the approximations to derive params which best suit your application. 
18th June 2013, 10:38 PM  #2 
diyAudio Member

For the linear part of the curve:
Id=KP*((2(VgsVto)*Vds)Vds^2)*(1+ Lambda*Vds) Good at first crack, but Vgs really isn't Vgs as RS gets in the way. What I've done is create an effective Vgs by multiplying the observed drain current by an approximated RS. Then let "Solver" find Vto, kappa, lambda and RS. Now, I'm wondering if it will work! 
19th June 2013, 02:44 PM  #3  
diyAudio Member

Quote:
FWIW, the datasheets and IRF's spice models don't seem to agree except for the first couple of Vgs series above Vto 

20th April 2015, 10:09 PM  #4 
diyAudio Member
Join Date: Dec 2011

Thanks for the work. I'm looking into using this for another FET; would you be able to attach or post a link to the spreadsheet, so that I can understand how you calculate error, etc? Thanks!

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