[SI-LIST] Re: Regarding rising waveforms in the IBIS models

Historically, they are very likely to be different.  The peak to peak
amplitude depends on the output impedance of the buffer.  In one case, the R
to ground the pullup device is active controlling the amplitude of the
swing.  In the case of R to Vcc the pulldown device is controlling the
amplitude.  In most cases the pullup and pulldown devices do not have the
same DC output impedance so the amplitudes will differ.  I have noticed in
more modern processes the IV characteristics of the pullup and pulldown
better match each other.  This gives a more consistent output impedance,
independent of state, which makes serial termination easier to do.

Tom Dagostino
Teraspeed Consulting Group LLC
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Jayasree Nayar
Sent: Thursday, August 12, 2004 5:37 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Regarding rising waveforms in the IBIS models


Hi all,
        Would like to get your inputs regarding the following questions
I have regarding the rising waveforms in an IBIS model:
In an IBIS model, for the two rising waveforms , one with V_fixture= 0
and the other with V_fixture =Vcc, should the total swing (difference
between the maximum and minimum voltage values) be the same.

If so, what could be the reason that there is a difference in the voltge
swing between the two rising waveforms.

Please advise. Thank you.

regards
Jayasree


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