Re: [Qucs-help] qucs simulation issue: diode simulation

[Stefan J. <st...@gr...>]

Am Mi, 4.08.2010, 04:22 schrieb Anno Hermanns:

>   Hi guys:

Hello!

> Really love your qucs simulator, but then ran into something that does
> not appear to work.
>
> I am simulating a trivial diode I/V deck using a DC simulation.
> When I play around with the value of Vj, the junction potential, nothing
> happens -
> the diode turn on voltage does not move, diode current at a given
> voltage does not move,
> nothing moves.
>
> When I change the Is parameter, the current does change as expected.
>
> As Vj is the diode built-in voltage, this has got to be a bug, no?
>
> Details of my software and system:
> - Mac Pro Intel running Mac OS 10.5.8
> - Installed qucs 0.0.15 a few weeks ago
>     from the archive qucs-0.0.15-macosx-10.5-intel.pkg
>     found at http://sourceforge.net/projects/qucs/files/qucs-binary/
>
> Wild speculation:
> - the Vj parameter may not be passed correctly,
>      or may be mistyped VJ somewhere, or may be referenced as Vbi

The interpretion of Vj is often confusing, I agree.  BUT, Vj so called
built-in junction voltage is NOT considered in DC current calculations
in diode models, but in capacitance calculations.

In order to shift the "threshold" voltage of a diode best way to go is
to change the Is parameter as you already figured out.  Also the area
parameter can be used; since real Is = Area*Is...

Best regards, Stefan.