Subject: Modeling question

From: Jerry Hayes <[email-masked]>
Date: Fri, 01 Oct 1999 17:51:03 -0400

I am attempting to create a v2.1 ibis model for a driver that is
essentially an I/O_open_drain with internal pullup termination.
I have created various ibis models for this driver ... however none
of them are correlating well to spice due to the internal pullup.
Can anyone suggest the proper modeling technique for this type of
driver?  Helpful suggestions are greatly appreciated.

Thanks,
Jerry Hayes

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From: [email-masked]
Date: Fri, 01 Oct 1999 16:27:38 -0700

Jerry,
I think the problem is that the "pullup" part of the model is always
turned on. (IBIS simulators expect it to turn off during the falling
edge and this is probably happening by default in your model)

I have two ideas to try:

1) Remove the pullup, make the model, and then put the pullup in by hand
as a part of the shunt curve.

2) Make the model as regular but do not make a "pull-up" measurement (or
set it all to zero) and once again let the pull-up curve reside in the
shunt part of the model.

regards,
Jon Powell
Manager, High Speed Consulting Services, Viewlogic Systems

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From: Donald Telian <[email-masked]>
Date: Fri, 01 Oct 1999 16:55:08 -0700

Jerry,

You can hide the pullup in the PowerClamp, such as:

<smaller><smaller>[POWER Clamp Reference]                2.5V       NA   
    NA

[POWER Clamp]

-2.5V  16.67mA  NA  NA | Use: V= -1*[POWER Clamp Reference], I=([POWER
Clamp Reference]/resistor_value)

 0.0V      0mA  NA  NA 

 2.5V -16.67mA  NA  NA | Use: V=[POWER Clamp Reference], I= -1*([POWER
Clamp Reference]/resistor_value)

</smaller></smaller>

This example ties a 150 Ohm resistor to 2.5 volts and leaves it there
even if the output tri-states.

Donald Telian

CADENCE

At 05:51 PM 10/01/1999 -0400, Jerry Hayes wrote:

Donald Telian

Cadence Design Systems

phone: 408-944-7791

email: [email-masked]