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

Subject: RE: [IBIS-Users]DC Sweep for the pullup IV curve
From: Allen Chao (achao@synopsys.com)
Date: Mon Aug 18 2003 - 08:03:52 PDT

Next message: Muranyi, Arpad: "RE: [IBIS-Users]DC Sweep for the pullup IV curve"
Previous message: SUDHEER: "[IBIS-Users] ECL LVDS model"
In reply to: Muranyi, Arpad: "RE: [IBIS-Users]DC Sweep for the pullup IV curve"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

Hi Arpad,
Thanks for your fast reply... I just consulted further with the buffer
designer here. He said that this output is a high-speed data output and
instead of using Vcc (power-supply voltage) for the power clamp diode and
the pull-up transistor, we use a current source to drive the output to 0.4v
for signal high and simply turn off the transistors between current source
and the output for the low signal. (since the output is also connected to
another resistor and ground, the output will be grounded for the low
signal). As I described, there are not really pullup/pulldown transistors
and clamping devices.
My question is, can we still create an IBIS model for this output?

Thanks in advance,

Allen Chao

-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On
Behalf Of Muranyi, Arpad
Sent: Thursday, August 14, 2003 7:07 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

|------------------------------------------------------------------
|For help or to subscribe/unsubscribe, email majordomo@eda.org
|with just the appropriate command message(s) in the body:
|
| help
| subscribe ibis <optional e-mail address, if different>
| subscribe ibis-users <optional e-mail address, if different>
| unsubscribe ibis <optional e-mail address, if different>
| unsubscribe ibis-users <optional e-mail address, if different>
|
|or email a written request to ibis-request@eda.org.
|
|IBIS reflector archives exist under:
|
| http://www.eda.org/pub/ibis/email_archive/ Recent
| http://www.eda.org/pub/ibis/users_archive/ Recent
| http://www.eda.org/pub/ibis/email/ E-mail since 1993

Next message: Muranyi, Arpad: "RE: [IBIS-Users]DC Sweep for the pullup IV curve"
Previous message: SUDHEER: "[IBIS-Users] ECL LVDS model"
In reply to: Muranyi, Arpad: "RE: [IBIS-Users]DC Sweep for the pullup IV curve"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

This archive was generated by hypermail 2b28 : Mon Aug 18 2003 - 08:10:02 PDT