Subject: RE: [IBIS] Terminated buffer
From: Tom Dagostino (tom@teraspeed.com)
Date: Thu Oct 10 2002 - 17:57:36 PDT
With IBS models you are trying to model the component as it would be used in
the normal environment. In the case you mention the actual driver would see
the internal pull up plus the load of the trace on the board, typically 50
Ohms or so. So when you model the driver it should have the "external" 50
Ohms loaded when simulating for the rising and falling waveforms.
Tom Dagostino
Device Modeling Division
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 430-1065
tom@teraspeed.com
http://www.teraspeed.com
-----Original Message-----
From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org]On
Behalf Of Shee Kian Wong
Sent: Thursday, October 10, 2002 4:40 PM
To: 'Ingraham, Andrew'
Cc: ibis@server.eda.org
Subject: RE: [IBIS] Terminated buffer
Hi all,
Normally we would use a 50ohms resistor and connect it to the output node to
get rising/falling data. However, if the built-in resistor is 50 ohms, and
we connect the IBIS load resistor (another 50ohms) to vcc, are we not going
to get an effective resistance that is lower that 50 ohms?
Confused,
Shee Kian
-----Original Message-----
From: Ingraham, Andrew [mailto:Andrew.Ingraham@hp.com]
Sent: Thursday, October 10, 2002 8:39 PM
To: Shee Kian Wong
Cc: ibis@eda.org
Subject: RE: [IBIS] Terminated buffer
The Pullup and/or Pulldown clamp I-V curves should describe anything that is
always in the circuit, including leakage currents, terminations, etc.
If the termination is independent of the supply, put it into the Pulldown
curve. If it tracks with the supply, use the Pullup curve, or a combination
of both.
Regards,
Andy
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