pb with spice3f4 and ngspice


To ng-spice@ieee.ing.uniroma1.it
From routoure Jean-Marc <routoure@lei.ismra.fr>
Date Thu, 15 Mar 2001 18:56:14 +0100
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Reply-To ng-spice@ieee.ing.uniroma1.it


Hi,

I find a little bug in ngspice ans spice3f4. 

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

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