Re: [IBIS-Users] Modeling input receivers with on-die termination


Subject: Re: [IBIS-Users] Modeling input receivers with on-die termination
From: Kim Helliwell (kimgh@apple.com)
Date: Fri May 09 2003 - 11:15:24 PDT


Tom:

I completely agree with making the models correct.
Todd was answering my earlier question of what to
do when a vendor supplied model is NOT correct.
For that case, a band aid is needed, particularly when
the vendor is recalcitrant about fixing the model...

On Friday, May 9, 2003, at 10:19 AM, Tom Dagostino wrote:

> This sounds like a band aid, not a solution. Let's make the models
> correct
> and not double count the currents.
>
> Tom Dagostino
> Teraspeed Consulting Group LLC Teraspeed Consulting Group LLC
> 2926 SE Yamhill St. Device Modeling Division
> Portland, OR 97214 13610 SW Harness Lane
> Beaverton, OR 97008
> http://www.teraspeed.com 503-430-1065
> tom@teraspeed.com
>
>
> -----Original Message-----
> From: owner-ibis-users@server.eda.org
> [mailto:owner-ibis-users@server.eda.org]On Behalf Of Todd Westerhoff
> Sent: Friday, May 09, 2003 8:06 AM
> To: Ibis-Users (E-mail)
> Subject: RE: [IBIS-Users] Modeling input receivers with on-die
> termination
>
>
> Kim, et al,
>
> I'm a little surprised that none of the tool vendors have checked in
> by this
> point. I've had users tell me what the different tools do, but no
> word from
> the tool-makers themselves.
>
> It seems to me the rub is that s2ibis2 assumes the clamp curves will be
> "added" one way (which is backed up, at least partially, by the IBIS
> spec,
> as noted by Stephen) - and the simulators do something else by
> extrapolating
> the power clamp curve. Simply put, s2ibis2 assumes that clamp current
> should be zero if voltage point is not specified in the particular
> clamp
> curve - the simulators do not.
>
> There is a different algorithm the simulators could use to avoid double
> counting with the existing models:
>
> 1. Check the input voltage
> 2. If the input voltage, <=VDDQ, look at the ground clamp curve first.
> Otherwise, look at the power clamp curve first.
> 3. If the voltage point exists in the curve you're looking at, use the
> corresponding entry for the current. Done. (this takes care out
> double-counting and the overlap case)
> 4. If the voltage point does not exist in the first curve, check the
> second.
> If the voltage point exists, take the corresponding current value.
> Done.
> 5. Only when the voltage point exists in neither curve (the gap case),
> extend
> each curve by extrapolation to find the current at the point in
> question.
> This will provide two (potentially slightly different) current
> values -
> use the average of the two.
>
> If the simulators worked this way, we wouldn't have to change s2ibis2
> at all
> (or, so it seems to me). The proposal 1 technique from my original
> mail
> would still work, but proposal 2 would need to be modified so that the
> individual curves ended once they hit the zero current point.
>
> 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"
>
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Kim Helliwell
Apple Computer
kimgh@apple.com
408 974 9936

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