RE: [IBIS-Users] on-die termination ... one more time

From: Muranyi, Arpad <arpad.muranyi_ f rom> Date: Thu Feb 17 2005 - 11:51:15 PST · This archive was generated by hypermail 2.1.8 : Thu Feb 17 2005 - 11:52:31 PST

I would like to answer the question:  "what is the cause for this Warning".

The warning says that the I-V curve never reaches zero current.  Picture
this in your mind, and try to explain it what this means if you wanted to
implement a circuit that does this.

Let's try with a Thevenin circuit, a voltage source and a resistor.  The
I-V curve of this circuit is a straight line crossing the voltage axis
at the voltage of the Thevenin source.  (This is when the current is zero,
and the resistor has zero volts across it).  The fact that the I-V curves
of IBIS models usually cross the origin, or the Vcc voltage rail means
that the pullup and pulldown devices are tied to those voltages,
respectively.

An I-V curve that never crosses the voltage axis in the range you are
plotting, boils down to a circuit in which there is a device that pulls
to a voltage that is outside the voltage range you are plotting.  In IBIS
most I-V curves go from -Vcc to 2Vcc.  It would be difficult (but not
impossible) to make a circuit that pulls to a voltage outside that voltage
range.  That's why the parser gives you a warning for such I-V curves.

Arpad Muranyi
Intel Corporation
============================================================================

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf Of Tom Dagostino
Sent: Thursday, February 17, 2005 11:24 AM
To: RODRIGUEZ_LECONA_RAMIRO; ibis-users@eda.org; ibis-info@eda.org
Subject: RE: [IBIS-Users] on-die termination ... one more time

It would be better to put a pull up resistor in the powerclamp and for
completeness any pulldown resistor would go in the groundclamp.  That way
the warnings to away.

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, February 17, 2005 11:02 AM
To: ibis-users@eda.org; ibis-info@eda.org
Subject: [IBIS-Users] on-die termination ... one more time

Hi all,

    Thank you by your answers. I am generating an IBIS model that includes
an input structure with a pull-up resistor. I include the pull-up resistor
characteristics in the ground clamp curve but when I check the IBIS file
with IBIS parser (IBISCHK3 v3.2.9) the parser  gives the warning: "WARNING -
Model Input02: GND Clamp : Maximum value never becomes zero".
    Michael Mirmak said that there is no requirement for all clamp curves to
"reach the zero value" then what is the cause for this Warning?

                                      Thank you

Best Regards

Ramiro
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