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A typical entry line in LTspice's Standard.bjt file contains, e.g.,

.model 2N4126 PNP(Is=1.41f Xti=3 Eg=1.11 Vaf=18.7 Bf=203.7 Ne=1.5 Ise=0 Ikf=80m Xtb=1.5 Br=4.924 Nc=2 Isc=0 Ikr=0 Rc=2.5 Cjc=9.728p Mjc=.5776 Vjc=.75 Fc=.5 Cje=8.063p Mje=.3677 Vje=.75 Tr=33.23n Tf=179.3p Itf=.4 Vtf=4 Xtf=6 Rb=10 Rb=10 Vceo=25 Icrating=200m mfg=Fairchild)

The product manual makes it very clear about what those parameters mean, but it is silent about where they could be found. Datasheets like this one seem to be of little or no use.

I assume these parameters must be somehow calculated to fit the Gummel & Poon model, but the question is: how? Is there a way, departing from ordinary data in a datasheet? Any existing spreadsheet? Some literature?

It can also be observed in the database that some transistors have more parameters than others. I wonder why.

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    \$\begingroup\$ In my experience these parameters are generated from fitting a multitude of equations to many, many measured datapoints. Your best approach is to get a SPICE model of the transistor in question from the manufacturer. \$\endgroup\$
    – Elliot Alderson
    Commented Jan 12, 2023 at 19:43
  • \$\begingroup\$ @ElliotAlderson In fact my (improved) BJT database has more transistors than I'll ever need, but some BJTs are difficult to get hold of, e.g. the 2SD637. It would be good though to find SPICE models for every transistor if I could. However, I found what seems to be a useful spreadsheet at brakken.no/el2/avgrensa/excel/excel.htm . I will see what I can do with it. \$\endgroup\$
    – Carlos Gouveia
    Commented Jan 12, 2023 at 19:59
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    \$\begingroup\$ See my answer here for a couple textbooks which contain parameter extraction techniques: electronics.stackexchange.com/a/538808 \$\endgroup\$
    – Ste Kulov
    Commented Jan 12, 2023 at 20:20

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