Subject: RE: [IBIS] ECL Termination Voltage Question
From: Tom Dagostino (tom@teraspeed.com)
Date: Thu Jan 15 2004 - 18:50:26 PST
If VT waveforms are present in the model the Ramp data is not used for the
main simulation but is sometimes used by auxiliary functions in the
simulator.
Tom Dagostino
Teraspeed Consulting Group LLC
Device Modeling Division
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@teraspeed.com <mailto:tom@teraspeed.com>
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
http://www.teraspeed.com
-----Original Message-----
From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org]On
Behalf Of Michael Sachtjen
Sent: Thursday, January 15, 2004 4:24 PM
To: Bob Ross
Cc: 'ibis@eda.org'; 'ibis-users@eda.org'
Subject: Re: [IBIS] ECL Termination Voltage Question
Bob,
You have a lot more experience with IBIS than I, but
your statement "[Ramp] is not used when you have V-T
tables" seem misleading. It's my understanding that
the simulators (Cadence at least) need to know the
switching time and dV from the [Ramp] even though
waveforms are provided? Please correct me if I'm
wrong.
I don't mean to confuse the issue; I know this thread
is not about the Ramp. I only want to clearify that
you can't just put 1/1 in for the ramp if you have V-T
tables.
- Mike
--- Bob Ross <bob@teraspeed.com> wrote:
> Hi Tom:
>
> The preset Vtt is not a problem because it is for
> the [Ramp]
> only, and the [Ramp] is not used when you have V-T
> tables.
>
> The switching shape problem was based on another
> issue which we
> have been we been communicating with you privately.
>
> Since the application is differential with 100 ohms
> differential
> and 200 ohms to GND, a better V-T specification
> would still
> be using the single-ended V-fixture to some
> equivalent Vtt
> voltage and the R_fixture at around 50 ohms or
> lower. This
> will be closer to the actual differential switching
> conditions
> for the V-T waveform extractions and specifications.
>
> Bob
>
>
>
>
> Fisher, Thomas wrote:
>
> > Bob, thanks for the response. Do I understand you
> correctly in that the
> > Vtt is pre-set (base on Vcc) within the model
> type, output_ECL? If
> > this is the case, then it creates a problem for
> this particular model.
> >
> >
> >
> > Secondly, I am using the [Rising Waveform] and
> [Falling Waveform] but it
> > does not correct this problem. The VT tables are
> created from Spice
> > with 200 ohm resistors to ground. If output_ECL
> is wanting to use the
> > pre-set Vtt = Vcc - 2V with 50 ohm resistors, this
> is a problem.
> >
> >
> >
> > Who could I contact that could explain how the
> output_ECL model type
> > is constructed? Thanks. T-
> >
> >
> >
> >
> >
> >
> >
> > Regards,
> >
> > Thomas Fisher
> >
> > Senior Systems Engineer
> >
> > Texas Instruments, Inc. Business: 214
> 480-3736
> >
> > P.O. Box 660199 MS8710 Fax: 214
> 480-3160
> >
> > Dallas, TX 75266-0199 tomfisher@ti.com
> <mailto:tomfisher@ti.com>
> >
> >
> >
> >
> >
> > Tom:
> >
> > My responses are in your text.
> >
> > Bob
> >
> > Fisher, Thomas wrote:
> >
> >> All,
> > >
> > > I have a PECL driver that I am modeling that
> has a non-standard load (pi
> > > network to ground) which results in a larger
> Vod. (1.2-V vs. 800mV)
> > > What happens during simulation is the
> single-ended waveform depicts a
> > > slowness of the rising edge which results in a
> plateau effect on the
> > > rise/fall of the differential waveform. (It
> looks great when simulating
> > > in TISpice) Most (P)ECL termination is going to
> be 50 ohms to Vtt for
> > > both non-inverting and inverting outputs
> whereas Vtt = Vcc 2-V. Under
> > > the load I am simulating we are using 200 ohms
> to ground. (customers
> > > request)
> > >
> > >
> > >
> > > Having said that, looking in the 3.2 spec on
> page 78 under ramp rates
> > > model_type for output_ECL it mentions 50 ohm
> resistor to the termination
> > > voltage (Vterm = Vcc 2-V). Is this Vterm
> embedded into the
> > > specification?
> >
> > Yes
> >
> > Is there a way to specify that the load is 200
> ohms to
> >> ground?
> >
> > Yes, but you must use the [Rising Waveform] and
> [Falling Waveform]
> > method and describe the waveform. This will
> override the [Ramp]
> > keyword, which cannot correctly specify the
> situation you describe.
> >
> > I believe this might be causing the abnormality.
> Any
> >> help/insight would be appreciated. Thanks in
> advance.
> >>
> >>
> >>
> >> Regards,
> >>
> >> Tom Fisher
> >>
> >>
> >>
> >
> > --
> >
> > Bob Ross
> >
> > Teraspeed Consulting Group LLC Teraspeed
> Consulting Group LLC
> >
> > 2926 SE Yamhill St. Device Modeling
> Division
> >
> > Portland, OR 97214 13610 SW
> Harness Lane
> >
> > 503-239-5536 Beaverton, OR
> 97008
> >
> > http://www.teraspeed.com 503-430-1065
> >
> > bob@teraspeed.com
>
<mailto:bob@teraspeed.com?subject=Re:%20%5bIBIS%5d%20ECL%20Termination%20Vol
tage%20Question&replyto=40042324.90405@teraspeed.com>
> 503-246-8048 Direct
> >
> >
>
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