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From:	"Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Date:	Wed, 31 Aug 2016 03:16:26 +0000
Message-ID:	<CAM2RGhSb3-KdN3rMo5vxjkbTO+-vU_Tgj+hOcoHxyz4HGwnzbA@mail.gmail.com>
Subject:	Re: [geda-user] Microwave PCB layout simulation or How to eat all
	your processing power in 3 easy steps
To:	gEDA users mailing list <geda-user AT delorie DOT com>
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On Sat, Aug 27, 2016 at 5:31 AM, al davis <ad252 AT freeelectron DOT net> wrote:
> On Sat, 27 Aug 2016 02:18:11 +0000
> "Evan Foss (evanfoss AT gmail DOT com) [via geda-user AT delorie DOT com]"
> <geda-user AT delorie DOT com> wrote:
>
>> How does gnucap-verilog solve this? I thought verilog was just another
>> language for describing netlists and schematic behavior.
>
> It is.  Verilog as a netlist format is much richer than the spice
> format.
>
> We have documentation on how to include the layout physical info in the
> Verilog netlist.
>
> First cut is here:
> http://gnucap.org/dokuwiki/doku.php?id=gnucap:user:netlist_import_and_export
>
> There is more detail and revisions in my FOSDEM presentation.
>
>
>> How does that
>> get us closer to testing a pcb level implementation of a Wilkinson
>> splitter or a distributed element filter? I would think we would need
>> FEM of some kind to extract the relevant properties of the layout and
>> then process them for conversion into verilog?
>
> The first step is to transfer the data.  Once the data is moved to a
> format that gnucap understands, the gnucap project can take it from
> there.

Reading the rest of your email that seems mostly like moving to
verilog is just a way of making the workflows graph simpler. Like
verilog ams is one container that we could use in place of a few other
ones.

I like gnucap but I don't want it to be the only tool that plugs into
the field solver stuff we add. Just like I would not want geda to only
support gnucap as it's one simulator. I would really like this to
continue with netlists as we have them. Xyce is a simulator that
supports gEDA like it is a thing they are proud of. Xyce is also nice
in that it works on distributed (MPI) environments. I want
compatibility and the choice to use Xyce or Gnucap depending on the
scale/type of problem.

> More detail. ...
>
> There are two parts here.
>
> One part is making a netlist, comprised
> mostly of transmission lines, or a more abstract device that is a
> transmission line underneath.

That is a simpler problem.

> The other part is to parameterize the
> transmission lines.  Initially, the parameters can be geometry.  There
> are simple closed form equations to generate electrical parameters that
> work well for simple structures.  Getting this far is a big
> accomplishment.

I doubt it will help the microwave people who really need a field solver.

> For more complex structures you need a field solver.
> There are free field solvers available.  (OpenEMS and others)  We just
> need to interface to them.

Antenna's, distributed element filters....

If we follow your plan we would still have to take the output of
openems and convert it back into an equivalent circuit for the
transmission line model. Cray LC did this but it is both unmaintained
(talked to the author) and closed source. I really like what you want
to do and it would be *very* useful to me.

> Hyperlynx actually uses a mix of field solver and closed form equations.

Hyperlynx is of no real interest to me. That was just used in one example.

> If what you want to see is radiation, you might be able to do it all
> with the field solver.

I would not want to do that. The processing power waste would be tremendous.

> For signal integrity, they all do it as a 2-step process, with one of
> the steps being a circuit simulator, usually not spice.

Ok. Well we have at least two users who can make good use of a field
solver on some antenna problems. Your solution already requires the
ability to export pcb-* geometry to a field solver. I could join your
project that is big and possibly get something done eventually or
continue with this smaller mission and help make something that works
now.

Sorry but I am already committed to various things for pcb-rnd any way.

-- 
Home
http://evanfoss.googlepages.com/
Work
http://forge.abcd.harvard.edu/gf/project/epl_engineering/wiki/

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