[SI-LIST] Re: Question on IBIS: rising/falling waveform - How complete waveform created?
- From: "Jack W.C. Lin" <JackWCLin@xxxxxxxxxxxx>
- To: "'arpad.muranyi@xxxxxxxxx'" <arpad.muranyi@xxxxxxxxx>,si-list@xxxxxxxxxxxxx
- Date: Fri, 24 Jan 2003 09:33:36 +0800
Hi Muranyi:
In theoretical, if we have pull up and pull down I-V curve (HIGH and LOW
curve) plus rise/fall time (ramp), the simulator should can create a
waveform. But this waveform will not the same as the waveform which is
created by simulator when include pull up, pull down, 4 sets V-T tables. I
can't understand that if we have I-V curve and ramp info, why we should have
4 sets V-T tables? Can you explain more about the roles of V-T tables? How
to help simulator to create more accurate waveform? I can't understand what
you said
" Mathematically, if you have a complementary buffer i.e. it has a
pullup and a pulldown, with four waveforms in the IBIS model you can set up
two equations with two unknowns for each edge (rise/fall)
and solve for the unknowns which are the coefficients vs. time for the
pullup and pulldown."
Thanks
Jack
-----Original Message-----
From: Muranyi, Arpad [mailto:arpad.muranyi@xxxxxxxxx]
Sent: Friday, January 24, 2003 12:18 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question on IBIS: rising/falling waveform - How
complete waveform created?
This is to answer Jack's and Adeel's questions about how waveforms
are used in IBIS.
To give an intuitive answer, you can think of waveforms as percentage
vs. time tables. They are telling the simulator is how to scale
the IV curves as a function of time as the buffer turns on/off.
Mathematically, if you have a complementary buffer i.e. it has a
pullup and a pulldown, with four waveforms in the IBIS model you
can set up two equations with two unknowns for each edge (rise/fall)
and solve for the unknowns which are the coefficients vs. time for
the pullup and pulldown.
Since the IV curve is a function of the pad voltage, the load of the
actual simulation doesn't have to be the same as the R_fixture that
was used for the waveform tables in the IBIS model. The actual
simulation waveform will adjust to the loading conditions.
I hope this helps to understand how the IBIS model works in simulators.
Arpad Muranyi
Intel Corporation
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