Subject: Re: [IBIS] ibis driver model for varied output impedance
From: John Angulo (jangulo@innoveda.com)
Date: Fri Mar 22 2002 - 18:56:56 PST
This posting is on behalf of Scott McMorrow. Please address any private
replies to him.
Ken,
An IBIS model is only able to have one operating point per model.
The general way to model this is to create multiple driver models with
different values for the impedance control resistor. For example,
one impedance point might be 50 ohms with a 2% resistor tolerance.
In that case the typical corner would be created with the nominal
process,
nominal temperature, nominal voltage and a 50 ohm impedance control
resistor. The minimum
corner case would be created with the slow process, high temperature
(assuming cmos),
minimum voltage and a 51 ohm (50 ohms + 2%) impedance control resistor.
The maximum
corner case would be created with the fast process, low temperature,
high voltage,
and a 49 ohm impedance control resistor. This information would be
enough to
create one model for the driver.
Multiple models can be created by choosing different impedance control
resistor
values as was done above.
Finally, the IBIS 3.2 Model Selector keyword can be used to allow
selection of
the different impedance models for the pins of the device. There are
several vendors
who have IBIS models that use this technique to model different driver
impedance
operating points. I believe that Intel may have some examples which are
publically available.
At SiQual, we have modeled quite a few drivers just as you describe for
our
clients and had very successful results.
best regards,
scott
-- Scott McMorrow Principal Engineer SiQual Interconnect Engineering 18735 SW Boones Ferry Road Tualatin, OR 97062-3090 (503) 885-1231 http://www.siqual.comKen Wu wrote:
> Hi there, > I have a question regarding ibis driver model for varied output > impedance. In one of my IOs, we can use a discrete resistor on PCB board > > to adjust the IO driver output impedance to match with board trace > impedance. This is neither a series resistor nor a parallel resistor > hooked > > up with the IO. It's a totally separate resistor and there is a > measurement circuit to measure the discrete resistor value and then > automatically > > adjust the IO output impedance based on the resistor value. My > question is, how does IBIS model to take care of this scenario? > > Regards, > > /Ken Z. Wu/ > /Force10 Networks, Inc/ > /ken@force10networks.com/ > /Tel: (408)571-3530/ > >
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