RE: [IBIS-Users] question about Cref

Different parts have different timing test loads associated with them.  They
are specified by the manufacturer and usually included in the datasheet.  If
the timing test load is just a capacitor, Cref then the model should have
that in it.  If the timing test load is a transmission line terminated in
its characteristic impedance to a voltage then you should put the Rref
resistance Ro to the termination Vref the termination voltage.  IBIS has no
way of describing a transmission line in the timing test load.

Tom Dagostino
Teraspeed Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
http://www.teraspeed.com
tom@teraspeed.com

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

Teraspeed is the registered service mark of
Teraspeed Consulting Group LLC

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of RODRIGUEZ_LECONA_RAMIRO
Sent: Thursday, April 14, 2005 2:53 PM
To: ibis-info@eda.org; ibis-users@eda.org
Subject: [IBIS-Users] question about Cref



    Hi all,

        In some cases the semiconductor vendors use a transmission line
terminated with a 50 ohms resistor to Vdd/2 in order to determine the
propagation delay or switching time of the devices. If the IBIS standard
says I have to specify Cref and the IBIS user wants to perform a timing
analysis, then,  is it necessary to specify Cref?

     Regards,

                         Ramiro.
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