Re: gEDA: gaf - Spice question

[Wojciech Kazubski <wk-at-NOSPAMire_dot_pw_dot_edu_dot_pl>]

Hi Magnus and All!
>
> Hi Wojciech,
>
> Just *how* broken is the current backend for your purposes?

The limitation to one device model is the most important (for all). For me (I 
am an RF engineer) the possibility to model a device as subcircuit (eg. with 
case parasitics) is important. So far I create spice files manually. 
Ideally the circuit drawn for spice modelling should be a block cut from the 
schematics with only the supply/signal sources and load resistors added.

> I am not saying that doing a separate backend (from fresh or reusing
> some code) is a bad thing, I just like to hear the arguments spelled
> out.

I think that both versions could be quite different but that do not mean that 
they will be totally different.
 
IC designers use the same transistor (or a few) with different scaling 
thruout the whole design, so the traditional spice approach is sufficient. 
This is already done for MOS transistors, they are treated in special way by 
current spice backend. Something similar can be done for bipolar transistors, 
FETs and diodes. So the current backend could be modified to do this if 
backward compatibility is not the problem.

The modification for circuit designers would be much more extent and probably 
will need some more functionality from gnetlist. Some more problems should be 
solved. This incude following:
- how to select a proper file to include for given device (by name or by a 
database)?
- what to do if the library contains models for many devices (select a part 
of it or include whole file)?
- how to avoid including the same model several times?
- to embed the model in a *.cir file or as an include file?
- what to do with components with multiple slots?
So there is much mowe work to do.

I looked into some web pages of semiconductor companies and found quite 
different copyrights ranging from  close to open source (NS) to "do not 
transfer any part of model outside your company" guarded by a registration 
form (Fairchild). I think that we can make a library of popular parts made 
ready for geda/spice modelling. Plus the guide how the proper model should 
look like.

W. Kazubski