Varactor Library Issues and ngspice limitations

[tomhajjar]

Having issues testing the "new" Varactor library and making a new one that includes packaging parasitics.

The "new" Library has issues. The Cjo, Vj, M and Rs values don't produce CV plots matching data sheets. This is not a big issue but it is worth trying to improve accuracy. Unfortunately I can't find Spice data for most of the devices so finding new values of Cj0, Vj and M would require experimentation. Qucs doesn't list the range Vj and M can vary. See comment on ngspice below for more on this.

Making a new Library using modern devices I found that ngspice has limits on Vj and M which won't allow using manufacture's Spice model values. Started a new ngspice topic. We will see.

https://sourceforge.net/p/ngspice/discussion/120973/thread/0153c4940e/

[tomhajjar]

@ra3xdh

Holger is working on the issue. He is leaning toward issuing warnings and not having hard limits.

Qucsator issues a warning about M for one specific diode but I don't know if it substitutes a default value like ngspice. I didn't dig into the source.

LTspice resolved this issue a decade ago.

[tomhajjar]

The latest ngspice nightly release now allows much higher VJ and M values.

https://ngspice.sourceforge.io/download.html#nightly