RE: [IBIS-Users] Problem in IBIS development

From: Tom Dagostino <tom_at_.....>
Date: Mon Jun 23 2008 - 09:14:00 PDT
Amit

The problem you are having is you are treating an open sink driver as a normal totem pole driver.  The normal open sink has a pulldown device only.  And in your case you have a pullup resistor tied to Vdd.  You are treating the pullup resistor as a pullup transistor.  Pullup transistors switch between off in the low state and on in the high state.  But a pullup resistor is always present in the circuit, it is always pulling up the load.  The pullup resistor belongs in the powerclamp table.  The driver type should be open sink or open drain, not output.

Regards,

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@teraspeed.com
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827 

-----Original Message-----
From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Amit KUMAR
Sent: Monday, June 23, 2008 4:22 AM
To: ibis-users@server.eda.org; ibis@server.eda.org
Subject: [IBIS-Users] Problem in IBIS development

Hello Experts,

I am developing IBIS model for a cell which is NMOS open drain type.
I have configured it as an output ibis model as the pullup resitor and pullup voltage values are fixed.
The problem is that the spice curve is not smooth and there seems to be sudden change in voltage around 1.4 Volts.
The ibis simulator is not able to replicate this behaviour.
The comparison between spice and ibis with load=30pf is attached with this mail with the name spicevsibis.
I have tried a lot but this behaviour of spice is not reproduced by ibis.

I am attaching the ibis file I have developed with this mail.
Kindly tell me what can be done to improve the performance of this ibis file.


Thanks and Regards
Amit

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Received on Mon Jun 23 09:15:32 2008

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