Subject: RE: [IBIS] Rsing/Falling/Ramp
From: Ingraham, Andrew (Andrew.Ingraham@hp.com)
Date: Thu Dec 05 2002 - 04:53:51 PST
> Normally there are 2 sets of rising/falling (1 set for 50W to gnd and 1 set for 50W to vcc) plus 1 ramp data in an IBIS file.
>
> Which one does a simulator use? The ramp or the rising/falling data? If rising/ falling data is used, which set (there are normally >1 set of data) would be chosen?
That depends entirely on the simulator.
I would expect most simulators to use the Waveform data,
if they are capable of using it. Some simulators might even
use both.
The first implementation of IBIS models integrated into Hspice,
used only the Ramp data.
In general, a simulator needs to employ some "magic" (a
complicated algorithm) to get from the Waveform data to
actual driven waveforms, because the real load rarely if ever
is a perfect 50 ohm resistor to VCC or to GND. A good
algorithm might use all available Waveform tables, appropriately
weighted, depending on actual load conditions. Again, I expect
this to be simulator dependent. (I believe that Hspice now can
use either one, or two, Waveform tables, but not more than the
first two tables it finds in the IBIS data sheet. You get to tell it
whether to use one or two.)
Regards,
Andy
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