Subject: [IBIS-Users] Re: [IBIS] ECL Termination Voltage Question
From: Michael Sachtjen (walldrug1316mi@yahoo.com)
Date: Thu Jan 15 2004 - 16:23:59 PST
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%20Voltage%20Question&replyto=40042324.90405@teraspeed.com>
> 503-246-8048 Direct
> >
> >
>
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