Message: 6
Date: Tue, 14 Aug 2007 13:21:53 -0600
From: John Doty <jpd@xxxxxxxxxxxxx>
Subject: Re: gEDA-user: Basic questions from a gEDA & Linux noob
To: gEDA user mailing list <
geda-user@xxxxxxxxxxxxxx>
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On Aug 13, 2007, at 11:45 PM, Felix Fujishiro wrote:
> On Mon, 13 Aug 2007 07:43:42PM -0700, Ben Jackson wrote:
>
> >On Mon, Aug 13, 2007 at 07:33:40PM -0700, Felix Fujishiro wrote:
> >>
> >> I tried to do this by adding the 'net=GND:4' attribute, and that
> works, but
> >> only if pin #4 is visible.
> >
> >I'm not sure what you mean. My Altera FLEX board used a chip-shaped
> >symbol with all the power and gnd hidden using net= attributes.
> There
> >are no pins for those anywhere.
>
> I guess I'm not being clear.... I'm using gschem for custom digital
> IC design, perhaps there's a difference in the way the tool treats
> MOS components and PCB components? If I remove pin #4 (the
> substrate/well connection) from the MOS symbol, gnetlist spits out
> a three-terminal device instead of a four-terminal device (which I
> want).
>
Which back end are you using? Perhaps spice-sdb? If so, I think I
understand what's going on.
Spice-sdb assigns pins by their pinseq= attributes, while the net=
attribute works on pin number. Without a pin, you have no place to
hang a pinseq= attribute, so spice-sdb won't understand that it needs
to make a connection.
If you're not adjusting transistor parameters much you could make
three terminal .SUBCKT models, each containing a single transistor,
with the substrate connected to a global node. Use model-name= (and
maybe file=, depending on how you organize things) to associate the
symbol with the subcircuit. The problem here for me would be that I
do mixed signal VLSI and I'm often tweaking individual transistor
parameters (L, W, M). In the subcircuit approach, you need a
different subcircuit for every geometry.
So for my work I just use the four terminal symbols and connect the
substrate node explicitly. I have very small VSS and VDD symbols for
this purpose. And I generally just box select and copy components in
preference to the dialog, so I can copy the transistor+substrate
combo together.
John Doty Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx
Yes John, I'm using spice-sdb for the back-end. At some point, I'd like to use gnetman instead of gnetlist, but I've been unsuccessful in installing it to my system.
Your suggestion to create a set of .SUBCKT models would probably work, but unfortunately I need to use a variety of L, W, and sometimes M. Would it be possible to include them as parameters in the .SUBCKT call, to avoid the problem of creating different subcircuits for each geometry?
The very small Vss and Vdd symbols you use might also work. I just don't like any extraneous clutter in the schematic, as I prefer them to be easy to read and comprehend quickly.
Message: 7
Date: Tue, 14 Aug 2007 15:28:35 -0400
From: al davis <ad151@xxxxxxxxxxxxxxxx>
Subject: Re: gEDA-user: Basic questions from a gEDA & Linux noob
To:
geda-user@xxxxxxxxxxxxxx
Message-ID: <200708141528.35379.ad151@xxxxxxxxxxxxxxxx>
Content-Type: text/plain; charset="iso-8859-1"
On Tuesday 14 August 2007, John Doty wrote:
> If you're not adjusting transistor parameters much you could
> make ? three terminal .SUBCKT models, each containing a
> single transistor, with the substrate connected to a global
> node. Use model-name= (and maybe file=, depending on how you
> organize things) to associate the symbol with the subcircuit.
> The problem here for me would be that I do mixed signal VLSI
> and I'm often tweaking individual transistor parameters (L,
> W, M). In the subcircuit approach, you need a different
> subcircuit for every geometry.
If you are adjusting transistor parameters, you can use gnucap.
You can change them any time with a ".param" statement, and
pass arguments to a .subckt.
Ah, thank you Al. I think you answered the question I just posed to John. I'll have to check out gnucap.
Thank you to you both for your help!
Felix