RE: [IBIS-Users]DC Sweep for the pullup IV curve

Subject: RE: [IBIS-Users]DC Sweep for the pullup IV curve
From: Tom Dagostino (tom@teraspeed.com)
Date: Thu Aug 14 2003 - 16:28:15 PDT

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One thing you need to consider. This part (which I have no knowledge of)
may only swing from 0 to 0.4 but if it is placed with another part on the
same net that can swing further you should cover a wider region in your
model. BTW, what logic family is this?

Tom Dagostino
Teraspeed Consulting Group LLC Teraspeed Consulting Group LLC
2926 SE Yamhill St. Device Modeling Division
Portland, OR 97214 13610 SW Harness Lane
Beaverton, OR 97008
http://www.teraspeed.com 503-430-1065
tom@teraspeed.com

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Muranyi, Arpad
Sent: Thursday, August 14, 2003 4:07 PM
To: ibis-users@eda.org
Subject: RE: [IBIS-Users]DC Sweep for the pullup IV curve

Allen,

Strictly speaking the spec says the following:

| The stated voltage ranges for I-V tables cover the most common, single
| supply cases. When multiple supplies are specified, the voltages shall
| extend similarly to values that handle practical extremes in reflected
wave
| simulations.
|
...
| 2) Voltage Ranges:
| Points for each table must span the voltages listed below:
|
| Table Low Voltage High Voltage
| ----------- ----------- ------------
| [Pulldown] GND - POWER POWER + POWER
| [Pullup] GND - POWER POWER + POWER
| [GND Clamp] GND - POWER GND + POWER
| [POWER Clamp] POWER POWER + POWER
| [Series Current] GND - POWER GND + POWER
| [Series MOSFET] GND GND + POWER
|
| As described in the [Pulldown Reference] keyword section, the I-V
tables
| of the [Pullup] and the [POWER Clamp] structures are 'Vcc relative',
| using the equation: Vtable = Vcc - Voutput.
|
| For example, a model with a 5 V power supply voltage should be
| characterized between (0 - 5) = -5 V and (5 + 5) = 10 V; and a model
with
| a 3.3 V power supply should be characterized between (0 - 3.3) = -3.3 V
| and (3.3 + 3.3) = 6.6 V for the [Pulldown] table.
|
| When tabulating output data for ECL type models, the voltage points
must
| span the range of Vcc to Vcc - 2.2 V. This range applies to both the
| [Pullup] and [Pulldown] tables. Note that this range applies ONLY when
| characterizing an ECL output.
|
| These voltage ranges must be spanned by the IBIS data. Data derived
from
| lab measurements may not be able to span these ranges as such and so
may
| need to be extrapolated to cover the full range. This data must not be
| left for the simulator to provide.

So according to the spec you would need to do -3.3 to 6.6 V. However,
this was written in the days when most buffers were switching rail to
rail, and most transmission lines were unterminated having a full
reflection.
The spec wanted to make sure that the IV curves would cover the voltage
range even if the waveforms double due to reflections.

Lately, the picture has changed, and we have more low voltage swing signals
and parallel terminated buses. As a consequence buffers do not necessarily
switch rail to rail, and reflections are much smaller. Even if we followed
the logic of full reflections, your model should be sufficient if it covered
-0.4 to 0.8 V. This would be officially not according to the spec, but
as far as I remember, the parser doesn't issue an error message, so you
should be OK.

I am dealing with similar situations in other cases too, and I am
actually considering writing a BIRD on this subject to clarify/change
the spec.

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

-----Original Message-----
From: Allen Chao [mailto:achao@synopsys.com]
Sent: Thursday, August 14, 2003 12:51 PM
To: ibis-users@eda.org
Subject: [IBIS-Users]DC Sweep for the pullup IV curve

Hi IBIS experts,
I have a question concerning the sweep. I have a 3.3V power supply for my
device. However, the logic high voltage is 0.4V and logic low is 0V for my
one of my outputs. Do I do the DC Sweep at the output from -3.3V to 6.6V
or -0.4V to 0.8V?

Thanks a lot for the help,

Allen Chao

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