RE: [IBIS-Users] Dynamic behaviour of buffer

Prabhat,
 
There may be two independent reasons for your
problem.  The capacitive loading is one, and
I have investigated that problem some time
ago:
 
http://www.vhdl.org/pub/ibis/summits/mar06/muranyi1.pdf
 
The other problem you may be facing is the
slew rate control feature in your buffer.
If this is designed with feedback from the
output pad, traditional IBIS models are not
going to be able to model it behaviorally.
 
Both of these problems could be overcome by
using one of the *-AMS language extensions of
IBIS, but you would have to come up with the
algorithms for them.
 
As Todd pointed out, another option is to revert
back to the SPICE model of the buffer if you have
enough time to wait for the simulations to get
done.  (SPICE tends to have a lot of detail and
therefore it can be very slow).  Most EDA vendors
I know of have support for various SPICE engines
in their PCB tools, including ours (Mentor).  You
do not need IBIS to bring in these SPICE models
into these tools.
 
Arpad
===================================================
 

________________________________

From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Prabhat Ranjan
Sent: Wednesday, August 27, 2008 2:29 PM
To: ibis-users@server.eda.org
Subject: [IBIS-Users] Dynamic behaviour of buffer


Hello Experts,
 
I have a driver with Slope control circuit at output pin. This circuit controls driver behaviour according to the Load on output pin.
 
IBIS model of this buffer has only R_fixture but when I am simulating IBIS model with certain capacitive load then IBIS is not able to produce exact SPICE behaviour.
 
My observation for mismatch is dynamic behavior of Slope control circuit with load which I am not able to model in IBIS.
 
My question is how can I model the dynamic behaviour of Slope control circuit in IBIS ?
 
Regards
Prabhat

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