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Re: [Help-gnucap] newbie: edit and BJT's

From: Al Davis
Subject: Re: [Help-gnucap] newbie: edit and BJT's
Date: Fri, 4 Oct 2002 02:08:35 -0600

On Wednesday 02 October 2002 07:21 am, Hugo van der Merwe wrote:
> I've recently started playing with gnucap (in the past I used
> ng-spice a little). Something I noticed as odd was this:
> Starting with a clean gnucap session, I type edit, and add
> e.g.:
>  Q1  1  2  3  4  tr2n2222
> Save, quit. Run edit again, it presents:
>  Q1  1  2  3  4  tr2n2222  area= 1.  icvbe= NA  icvce= NA
> temp= NA
> Seeing this doesn't surprise me, but exit the editor again:
>  ... 2  3  4  tr2n2222  area= 1.  icvbe= NA  icvce= NA  temp=
>                                          ^ ? what's this?
> Running edit again presents:
> Q1  1  2  3  4  tr2n2222  area= 1.  icvbe= 0.  icvce= NA
> temp= NA
> Quitting results in complaint about the next NA, and so it
> continues until all turn to "0". Curious.

This is a known bug in 0.31, fixed in 0.32, due out soon.

There are actually 2 bugs.  One is fixed.  The other remains.

The one that is fixed is that it no longer prints the "NA"
stuff.  It is in the BJT model code, actually in the file

The one that isn't fixed is what happens when reading an "NA"
in the input.  It won't read it as a number, giving zero as a
result, and doesn't eat it, leaving it to be interpreted as a
keyword, and then it doesn't match anything, giving the "what's
this" error message.

> The other thing, is there something clearly wrong and/or
> unimplemented in this model:
> *  Fairchild Semiconductor 2N3904
> .MODEL tr2N3904 NPN (Is=6.734f Xti=3 Eg=1.11 Vaf=74.03
> Bf=416.4 Ne=1.259 + Ise=6.734 Ikf=66.78m Xtb=1.5 Br=.7371
> Nc=2 Isc=0 Ikr=0 Rc=1 Cjc=3.638p Mjc=.3085 + Vjc=.75 Fc=.5
> Cje=4.493p Mje=.2593 Vje=.75 Tr=239.5n Tf=301.2p Itf=.4 Vtf=4
> Xtf=2 Rb=10)
> Both ng-spice and gnucap present very strange results when I
> use this in a cascode amplifier circuit instead of a 2N2222.
> (I can send this netlist if needed.)

I can't answer this one without a netlist.  Do ng-spice and
gnucap agree?  That is, give the same "strange" result?  How
about older versions of spice?  If so, that leads me to believe
there is something wrong with the parameters.

> That brings me to my last two question at this moment:
> Is there some place to find a nice summary of what has been
> implemented and what has not in terms of spice2/spice3
> compatibility?

No.  There should be, and will be.  It's called a "to-do" list.

> How far down the line might monte-carlo analysis be, years,
> or months?

Probably a long time, unless someone (you??) wants to help do

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