Subject: RE: [IBIS-Users]Difference in rise-fall waveform due to c_comp!!
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Tue Mar 02 2004 - 12:32:05 PST
Alok,
What you see is the correct behavior.
The meaning of C_comp is die capacitance which includes
everything that is on the die, pad, metal, transistors,
etc... When you obtain waveforms (Vt curves), this
capacitance is in place, so the waveform includes its
effects. For this reason, IBIS simulators do not use
this capacitance to load the waveform that is in the
IBIS model, i.e. no matter what value you provide for
C_comp, the simulation waveforms will remain the same
(within reasonable limits) with the same resistive
load on the output. On the other hand, any external
capacitance connected to the output of the IBIS model
will change its simulation waveforms, because that
will act as a load to the buffer.
On the other hand, the value of C_comp will have an effect
the reflections which come to the buffer from the outside.
In summary, C_comp is invisible from the inside out, but
visible from the outside in.
I hope this helps,
Arpad Muranyi
Intel Corporation
=========================================================
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Alok Rungta
Sent: Tuesday, March 02, 2004 8:57 AM
To: ibis-users@eda.org
Subject: [IBIS-Users]Difference in rise-fall waveform due to c_comp!!
Hello IBIS users,
I am trying to understand how the simulation tool is using the c_comp
parameter in the ibis model. For the same ibis model i just change the
c_comp parameter and resimulated to see if there are any differences in
the observed output voltage waveform. When using a cap as a load I see
differences in both the rise and the fall transition .. but when using
a pure resistive load I find that both the models on simulation give the
same rise waveform but different fall waveforms. Is this the expected
behavior ?? Isnt c_comp supposed to be used only in case of reflection ??
Thanks in Anticipation
Alok Rungta
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