Re: [ng-spice] pb with spice3f4 and ngspice


To ng-spice@ieee.ing.uniroma1.it
From "p.nenzi@ieee.org" <pnenzi@ieee.ing.uniroma1.it>
Date Sun, 15 Apr 2001 15:51:40 +0200 (CEST)
Delivered-To mailing list ng-spice@ieee.ing.uniroma1.it
In-Reply-To <01031519040601.02548@leipc8 >
Mailing-List contact ng-spice-help@ieee.ing.uniroma1.it; run by ezmlm
Reply-To ng-spice@ieee.ing.uniroma1.it


On Thu, 15 Mar 2001, routoure Jean-Marc wrote:

> 
> Hi,
> 
> I find a little bug in ngspice ans spice3f4. 


Correct, I have checked that on the latest CVS code. The bug seems to be
related with the way that spice uses for deriving a pmos model from an
nmos: it multiply some values by MOS1type which means: -1 for pmos and 1
for nmos. May be that the "show all" command do not show vds and vgs but
MOS1type*vgs and MOS1type*vds. This can be the cause of the error. 

Jean, can you work on this, while I try to do empty my TODO list applying
patches and integratong other models. Anyone, if have some spare time can
look if my explication of the bug is correct, so that I can close on all
the affected devices ?

Thanks a lot,
Paolo 


> 
> I use the following circuit to bias a PMOS (VG<0, VD<0) 
> 
> * a small circuit
> 
> M1 D G 0 0 monpmos w=5u l=1u
> 
> vd d 0 dc -5
> vg g 0 dc -10
> 
> .model monpmos pmos (KP=1e-6 VT0=-3.5 )
> 
> .end
> 
> 
> Using spice or ngspice in interactive: 
> ----------------------------------------------------------
> >source pmos.cir
> >op  
> 
> >show all
> 
> ngspice 3 -> show all
>  Mos1: Level 1 MOSfet model with Meyer capacitance model
>  device           m1
>  model       monpmos
>         id    0.0001
>         is   -0.0001
>         ig         0
>         ib -1.93e-12
>        vgs        10
>        vds         5
>        vbs        -0
>        von      -3.5
>      vdsat      -6.5
> ....
> 
> -------------------------------------------------
> 
> As you can see spice indicates that the vgs and vds voltages are positive !
> The problem also exists with spice opus.
> 
> Any idea where is the bug ?
> 
> JM
> 


Partial thread listing: