[SI-LIST] Re: IBIS modeling
- From: Scott McMorrow <scott@xxxxxxxxxxxxxxxx>
- To: jpowell@xxxxxxxxxxxx
- Date: Thu, 11 Oct 2001 16:45:04 -0700
It turns out that it is possible to create IBIS models for differential
drivers with quite good correlated results to SPICE differential
simulations. We've created quite a few using the following techniques:
1) The SPICE circuit used for extraction of the buffer I/V and V/T
curves must operate in a balanced mode at the correct operating
point.
2) Instantaneous common mode offset in the SPICE simulations must
be eliminated from the simulations prior to extraction. There are a
few methods available to accomplish this.
3) V/T extraction must be performed at the normal operating conditions
for the device, and be consistent with the operating conditions
of the I/V curve extractions. If this is not possible, then the I/V curves
must be
extracted from a transient simulation at the nominal operating point,
rather than a DC simulation.
4) The IBIS model is valid only over a small set of operating conditions
near the common mode operating point, because the IBIS model is inherently
single ended by construction. For multiple operating points, such as might
be seen in BLVDS applications or with non-100ohm system termination, multiple
IBIS model extractions would be necessary.
LVDS drivers are rather complex creatures and are generally extremely
"twitchy" to work with in SPICE. This tends to complicate the single ended
IBIS model extraction. In general, there is no one way to create an IBIS
model from a differential SPICE model. However, there are quite a few tricks
in the bag that can be used to create useful and highly accurate models.
best regards,
scott
--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR 97062-3090
(503) 885-1231
http://www.siqual.com
Jon Powell wrote:
> I have done some LVDS models and have NOT had any (good) luck
> in simulating them as single ended buffers.
> Let me re-phrase that. Most of the SPICE models that I have run do
> not give correct (or self-correlating) results if you don't put the
> series current return resistor into the LVDS circuit. If you try to
> simulate this resistor with a resistor to some constant node you also
> get bogus results. In order to get correct SPICE results you have to
> simulate
> both drivers at the same time with the correct termination.
>
> I have seen this result in 3 independent LVDS drivers from different
> vendors.
>
> For an example LVDS IBIS model, you might check out the National or Altera
> web pages.
>
> jon
>
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Chris Brewster
> > Sent: Thursday, October 11, 2001 10:32 AM
> > To: khalida@xxxxxxxxxxx
> > Cc: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: IBIS modeling
> >
> >
> > Khalid,
> >
> > Most of the information describes the process for extraction
> > of a Single
> > Ended buffer. With LVDS, you have to treat each output as if
> > it were a
> > single ended buffer and then combine them to create a
> > differential model.
> >
> > The literature from the IBIS summit by Hegazy is a good place
> > to start.
> >
> > http://www.eda.org/pub/ibis/summits/jan01/hegazy.zip
> >
> > regards,
> >
> > -Chris
> >
> >
> > At 09:01 AM 10/11/2001 -0700, Khalid Ansari wrote:
> >
> > >Hi all,
> > >
> > >I am looking to create IBIS models for my LVDS I/Os. I already
> > >have Hspice models created. Is there any good literature on how
> > >to create IBIS models out of Hspice models. I haven't had a chance
> > >to work with IBIS in the past so any introductory literature will be
> > >helpful. I guess the IBIS version I will be using is 3.2
> > with scripts
> > >created by North Carolina State University.
> > >
> > >Thanks in advance,
> > >Khalid
> > >
> > >------------------------------------------------------------------
> > >To unsubscribe from si-list:
> > >si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> > >
> > >or to administer your membership from a web page, go to:
> > >//www.freelists.org/webpage/si-list
> > >
> > >For help:
> > >si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> > >
> > >List archives are viewable at:
> > > //www.freelists.org/archives/si-list
> > >or at our remote archives:
> > > http://groups.yahoo.com/group/si-list/messages
> > >Old (prior to June 6, 2001) list archives are viewable at:
> > > http://www.qsl.net/wb6tpu
> > >
> >
> >
> > ------------------------------------------------------------------
> > To unsubscribe from si-list:
> > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
> >
> > or to administer your membership from a web page, go to:
> > //www.freelists.org/webpage/si-list
> >
> > For help:
> > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
> >
> > List archives are viewable at:
> > //www.freelists.org/archives/si-list
> > or at our remote archives:
> > http://groups.yahoo.com/group/si-list/messages
> > Old (prior to June 6, 2001) list archives are viewable at:
> > http://www.qsl.net/wb6tpu
> >
> >
> >
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
