Subject: RE: [IBIS-Users] RE: model issue for input receiver
From: Todd Westerhoff (twesterh@cisco.com)
Date: Thu May 01 2003 - 13:59:42 PDT
Fantastic!
Thanks,
Todd.
Todd Westerhoff
High Speed Design Specialist
Cisco Systems
1414 Massachusetts Ave - Boxboro, MA - 01719
email:twesterh@cisco.com
ph: 978-936-2149
============================================
"When did the choices get so hard, with so much more at stake?
Life gets mighty precious when there's less of it to waste"
- Bonnie Raitt, "Nick of Time"
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Muranyi, Arpad
Sent: Thursday, May 01, 2003 3:43 PM
To: Ibis-Users (E-mail)
Subject: RE: [IBIS-Users] RE: model issue for input receiver
Now that Bob brought up the "parallel" termination (which is actually
a totem-pole, double resistor termination between the power-I/O-ground
nodes), I would like to mention how I would do it. (This is not
explained in the IBIS class material I referenced in my previous posting
but is also implemented in IBIS Center).
From left to right, I keep the data up to the point where it reaches
zero current, and from there I cut off everything else to the right,
by replacing everything with zeroes. I do this in both the GND relative
and the Vcc relative data. While it is true that this kind of separation
does not separate the upper and lower resistor's values for the processed
data that goes into the IBIS model, it is still better than keeping
everything in just one clamp curve. In order to decompose the curves
into their true impedances, one would have to either do the measurements
differently or separate the two resistors in the netlist for the two
measurements.
Arpad
========================================================================
-----Original Message-----
From: Bob Ross [mailto:bob@teraspeed.com]
Sent: Thursday, May 01, 2003 10:11 AM
To: Todd Westerhoff
Cc: Ibis-Users (E-mail)
Subject: Re: [IBIS-Users] RE: model issue for input receiver
Todd:
The terminator characteristics should be put in the clamp from
which the terminator is referenced. A "pullup" terminator would
normally be in the [Power Clamp] table, and a "pulldown" terminator
would be in the [Gnd Clamp] table.
Usually data sheets give information on where terminators are
connected.
A parallel terminator should have its characteristics split
between both clamp tables. For example, a parallel terminator
constructed with two 100 ohm resistors should have a 100 ohm resistance
component in each clamp. Usually data sheet information is provided,
and sometimes some mathematical allocation of currents is needed.
I have not tested this, but it might be possible to extract terminator
components directly. For example, the Vcc terminal could be connected
to the I/O terminal to get the [Gnd Clamp] component of a parallel
terminator (by zeroing out the power clamp component). Similarly, the
Vss terminal could be connected to the I/O terminal for the
[Power Clamp] component. Both sweeps would be done in the High-Z
or Input mode.
To restate the point you make, while the [Gnd Clamp] and [Power Clamp]
sweep ranges IMPLY concatenation of the tables, the correct IBIS
interpretation is that both tables can extend over the entire
voltage range (by extrapolation), and that both table contributions
alway exist and the currents are always added. (In most devices without
internal terminators, the concatenation also works because the
currents and their slopes for extrapolation are 0.0.)
Bob
Todd Westerhoff wrote:
> Funny you should say that - we were just puzzling over this yesterday!
>
> Arpad - I agree with the statement that the terminator characteristics
> should be in one clamp curve or the other - the question is - how?
>
> If the input buffer truly uses on-die termination, then the DC sweeps you
> perform for BOTH the ground clamp and the power clamp will include the
> termination characteristics, correct? If you put those clamp curves in
the
> IBIS file as-is, won't you get twice the current (and therefore twice the
> termination strength) you bargained for?
>
> We were trying to figure out the right approach to de-embedding the
> termination effect from either one of the clamp curves - can you shed any
> light on this?
>
> Thanks,
>
> Todd.
>
> Todd Westerhoff
> High Speed Design Specialist
> Cisco Systems
> 1414 Massachusetts Ave - Boxboro, MA - 01719
> email:twesterh@cisco.com
> ph: 978-936-2149
> ============================================
>
> "When did the choices get so hard, with so much more at stake?
> Life gets mighty precious when there's less of it to waste"
>
> - Bonnie Raitt, "Nick of Time"
>
>
> -----Original Message-----
> From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
> Behalf Of Muranyi, Arpad
> Sent: Wednesday, April 30, 2003 6:41 PM
> To: Eric Hsu; Ibis-Users (E-mail)
> Cc: Frank Dunlap
> Subject: [IBIS-Users] RE: model issue for input receiver
>
>
> Eric,
>
> No. The reason is because the difference between a terminator and an
input
> is
> that the first one just terminates, and doesn't have Vinh and Vinl. If
you
> want to make an input model that also has an on-die terminator, you have
to
> put the terminator's characteristics into one or the other clamp IV
curves.
>
> Arpad
>
============================================================================
> ==
>
>
>> -----Original Message-----
>>From: Eric Hsu [mailto:ehsu@netlogicmicro.com]
>>Sent: Wednesday, April 30, 2003 3:33 PM
>>To: Ibis-Users (E-mail)
>>Cc: Frank Dunlap
>>Subject: model issue for input receiver
>>
>>Hi
>>
>>Can I choose "terminator" as my [model type] if I have an input receiver
>>
> with on die terminator? If true, can I also use subparameters [Vinh] and
> [Vinl] to define input threshold voltage? If true, then what is the
meaning
> of "...but has no digital logic thresholds..." for terminator model in
IBIS
> spec. 3.2 version, page20?
>
>>Best Regards,
>>
>>Eric Hsu
>>Interface Technologies
>>NetLogic Microsystems, Inc.
>>450 National Ave.
>>Mountain View, CA 94043
>>650-961-6676 x198
>>
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-- 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 503-246-8048 Direct|------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993 |------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993
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