RE: [IBIS-Users] RE: on-die termination

Rather you use a discrete resistor value (Rgnd,
Rpower) or include it in the IV clamps largely depends
on if the termination is linear, and if it can be
removed or turned off when you're characterizing the
rest of the buffer. If so, keep it simple, go with
the discrete. If not, you may need it to be included
in the clamp curves to be accurate.

--- Tom Dagostino <tom@teraspeed.com> wrote:

> A series resistor model works well for terminations
> and it avoids having to
> put it into the clamp characteristics. This also is
> the only way to do a
> differential termination. One end of the resistor
> is tied to the I/O pin of
> interest and the other end it tied to the ground,
> supply or diff pair pin.
> Also, it makes playing with the termination value
> very easy.
>
> Tom Dagostino
> Teraspeed Labs
> 13610 SW Harness Lane
> Beaverton, OR 97008
> 503-430-1065
> http://www.teraspeed.com
> tom@teraspeed.com
>
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> 401-284-1827
>
> Teraspeed is the registered service mark of
> Teraspeed Consulting Group LLC
>
> -----Original Message-----
> From: owner-ibis-users@eda.org
> [mailto:owner-ibis-users@eda.org]On
> Behalf Of Mirmak, Michael
> Sent: Monday, February 14, 2005 2:33 PM
> To: RODRIGUEZ_LECONA_RAMIRO; ibis-users@eda.org;
> ibis-info@eda.org
> Subject: [IBIS-Users] RE: on-die termination
>
>
>
> Ramiro,
>
> Thanks for your message and for your interest in
> IBIS. The standard
> approach I have seen is to add the on-die
> termination's effects into the
> clamp curves, as you mention. You should, of
> course, take steps to
> avoid "double-counting" of any single termination;
> in other words,
> ensure that the effects of any single terminating
> device are not present
> in both the [POWER Clamp] or [GND Clamp] keyword
> table data for the same
> voltage points.
>
> There is no requirement, per se, for all clamp
> curves to "reach the zero
> value" as you state. For example, I may include a
> pullup resistor's
> effects in the I-V table data for a model of type
> input. In this case,
> if the termination resistor and the power clamp
> diode(s) are both
> referenced to the same VCC supply, my IBIS model's
> [POWER Clamp] I-V
> curves will likely pass through the origin,
> VCC-referenced. The [GND
> Clamp] I-V curves will not cross through the origin
> (I will see a
> negative current at 0 V, ground-referenced, due to
> the current flow
> "out" of the pad), but there is nothing illegal in
> this. You would not
> be required to use terminators, Rpower or Rgnd in
> this case.
>
> I hope this helps!
>
> - Michael Mirmak
> Intel Corp.
> Chair, EIA IBIS Open Forum
>
>
> -----Original Message-----
> From: owner-ibis-info@eda.org
> [mailto:owner-ibis-info@eda.org] On Behalf
> Of RODRIGUEZ_LECONA_RAMIRO
> Sent: Monday, February 14, 2005 2:12 PM
> To: ibis-users@eda.org; ibis-info@eda.org
> Subject: on-die termination
>
>
> Hi all,
>
> How can I include on-die termination for an
> input structure in an
> IBIS
> model?
>
> Some people say that one way to include on-die
> termination is to
> use
> superposition and add the termination currents to
> the diode currents in
> the
> clamp sections. However this action is going to
> avoid that the clamp
> curves
> reach the zero value so the IBIS parser will report
> a error message.
>
> Do I have to use the keywords Rgnd and/or
> Rpower?
> When can I use "terminator" as my [model type]?
>
> Thanks.
> Ramiro
>
>
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Received on Mon Feb 14 16:19:10 2005