RE : IBIS differential model questions

Hi Syed and all,

  Though I don't quite get the meaning but I still want to express my
question and concern here, it sounds to me that the tools will use the
single ended characteristic to generate another leg, but we have some
drivers which I believe to be the differential drivers, for example, the USB
driver which has p0+ and p0-. And due to some pad pitch and layout
optimization problems, we are not able to make the driving and edge
rate...etc of the two legs exactly the same, so it is not accurate to derive
one leg from the other, then how should we do? Thanks for any input and
hope that I am not off the topic..

  Best Regards

ChingFu Chuang

> -----Original Message-----
> From: Syed Huq [SMTP:shuq@cisco.com]
> Sent: Wednesday, November 25, 1998 5:26 AM
> To: ibis-users@eda.org; j_martin@qlc.com
> Subject: Re: IBIS differential model questions
>
> John,
>
> Here are my thoughts on this. s2ibis2 or IBIS looks at a differential
> buffer
> as if it was a single ended buffer. So only one leg of the buffer output
> is
> modeled. Even the [Ramp] numbers are derived out of one single-ended
> output.
>
> It uses the [Diff pin] keyword to indicate the other leg of the Diff
> buffer.
> The simulators take info of the modeled single ended buffer and re-creates
> the
> other leg of the Diff buffer(using [Diff pin]).
>
> One problem here is the R_load gets tied to either Vdd or GND(based on
> test).
> There is no true differential load. You can get by by using the V/T table
> data
> and specifying V_fixture, R_fixture.
>
> So, in summary, for a Diff buffer, you create ONE IBIS model(single-ended)
> and
> use the [Diff pin] keyword to mention the other pin of the output.
>
> Regards,
> Syed
> Cisco Systems, Inc
>
> > From j_martin@qlc.com Mon Nov 23 14:30:37 1998
> > X-SMAP-Received-From: outside
> > From: John Martin <j_martin@qlc.com>
> > To: "'ibis-users@eda.org'" <ibis-users@eda.org>
> > Subject: IBIS differential model questions
> > Date: Mon, 23 Nov 1998 14:26:19 -0800
> >
> > I am trying to build a differential IBIS model. I am not aware of a way
> to
> > create a single IBIS model from a differential buffer which has two
> output
> > pins and two independent voltage sources. It does not seem logical to
> > create two IBIS models for one differential buffer, one for each output
> pin.
> > Is there a way to create a single IBIS model for a differential I/O
> buffer
> > using s2ibis2? I have read the section in the s2ibis2 manual that
> describes
> > the differential pin list and it states that s2ibis2 does not process
> any of
> > the information in that list, it simply copies it to the output file. I
> use
> > s2ibis2 for Solaris to create IBIS models.
> >
> > Thanks,
> > John Martin
> > QLogic Corporation
> >
Received on Tue Nov 24 18:52:31 1998