Subject: RE: [IBIS-Users] IBIS and HSPICE simulation result question
From: Jeremy Plunkett (jeremy@serverworks.com)
Date: Tue Mar 26 2002 - 11:34:02 PST
Gang,
the IBIS model clamps will only affect the level of overshoot when the model
you created is the receiver. If you are driving the model output into a
transmission line test load, the level of overshoot at the end of the line
will depend on the edge rate and output impedance of your IBIS model, but
not on the clamps.
I do a correlation check into a test load that matches the termination
conditions that the driver will see in use, and correlate the waveform at
_the driver's own output pad_ before looking at anything else. If the
driver will be used on a terminated bus like DDR or GTL, use a test load
that is a resistor equal to the transmission line impedance, connected to
the termination voltage level. If the driver will be driving from the
middle of a terminated bus, divide the transmission line impedance by two
since the driver actually drives 2 transmission lines in parallel. If the
driver will be used on unterminated lines, than the load should be a pullup
or pulldown resistor equal to the nominal trace impedance.
If your extraction was accurate, you should see near-perfect correlation of
the output waveform into these loads. In particular, if you do a
correlation into the same loads that are used for the IBIS model VT curves
(usually 50 ohms pullup and pulldown), and you don't see 99% perfect
correlation, then there is definitely a problem with either the model or
your simulation setup.
Good luck, hope this helped!
Jeremy
|>--/\/\/--((((((((()--|>
Jeremy Plunkett
Signal Integrity Engineer
ServerWorks Corp
www.serverworks.com
|>--/\/\/--((((((((()--|>
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On Behalf Of
Gang Huo
Sent: Monday, March 25, 2002 12:47 PM
To: ibis-users@eda.org
Subject: [IBIS-Users] IBIS and HSPICE simulation result question
Hi All,
When I try to correlate a IBIS I/O model simulation with HSPICE model
using HSPICE version 2000.4, the result is pretty good on the standard
load and open transmission line load. One thing concerns me is that in
the simulation of a load of transmission line to receiver simulation,
the overshoot level of the signal is much higher when using the IBIS
model than the HSPICE model, (the difference between two case is 0.5V
nominal and 0.7V in best case, this is a 3.3v I/O buffer).
I doubt this may be because of the clamp tables in the IBIS model. But
as the creator of the model, I am pretty confident that the clamp tables
in the IBIS model are correct, so can someone give me an idea what else
in the IBIS model may cause this? Will this cause a problem to the
users? And is there any good way to address this issue when creating the
models?
Thanks in advance,
Gang Huo
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