Subject: RE: [IBIS-Users] (lv)pecl
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Tue May 13 2003 - 09:37:27 PDT
Eric,
The question is not so much what the IBIS simulator does with the
clamp information, but what is the function of the clamps in real
life? If you understand the second part, you will also understand
the first.
The short answer is that it will clip signals that go beyond the
rails, hence the name "clamp". Regarding the resistance question,
usually the problem is that SPICE models do not include the resistive
properties of the diodes, so you get an ideal diode with no series
resistance. This resistance is usually in the low Ohms, but it
depends on the design. If you have a SPICE model that uses ideal
diodes, you can add a small value resistor in series with the diode
to avoid those high currents.
Arpad
===================================================================
-----Original Message-----
From: erik.van.der.ven@philips.com [mailto:erik.van.der.ven@philips.com]
Sent: Tuesday, May 13, 2003 1:50 AM
To: ibis-users@eda.org
Subject: RE: [IBIS-Users] (lv)pecl
As Tom and Fred suggest I have to add "some" resistance to the clamp diodes to prevent high currents. Must these device models be characterised or should I just add an arbitrary value. If so what will be the value of this information. I still don't have the insight what an IBIS simulator does do with the clamping info?
With kind regards,
Ir. Erik van der Ven
Room DB1032
Business Line Networking Infrastructure
Philips Semiconductors BV
Gerstweg 2
6534 AE Nijmegen
The Netherlands
Phone: +31-24-3534334
"Tom Dagostino" <tom@teraspeed.com>
05/12/03 06:41 PM
Please respond to tom
To: Erik van der Ven/NYM/SC/PHILIPS@EMEA2
<ibis-users@server.eda.org>
cc:
Subject: RE: [IBIS-Users] (lv)pecl
Classification:
Erik
Fred is right that for an ECL model that the voltage range that has to be characterized is over the 0 to Vcc - 2V range in the table. I like to see at least the active region between 0 and Vcc modeled. There are some ECL parts that will not be adequately characterized by only going from 0 to Vcc - 2V. If I remember correctly ON Semi makes some ECL line drivers that have about twice the swing of normal ECL.
Fred, the garbage Erik referred to was multiple lines in the tables that have the same voltage values and zero current. I've seen models with this before but I don't remember the cause of it.
Yes, IBIS likely goes too far into the clamp regions for characterization. If your clamp currents are extreme it is likely that the clamp diodes have not been properly characterized in their SPICE models. If you are seeing more than a few amperes in the clamps you can assume the intrinsic resistance of the diodes, the metal, etc. have not been fully characterized. To eliminate this try adding a few hundred milli Ohms in series with the clamps to bring the currents down to a more realistic level.
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@server.eda.org [mailto:owner-ibis-users@server.eda.org]On Behalf Of erik.van.der.ven@philips.com
Sent: Monday, May 12, 2003 1:44 AM
To: ibis-users@server.eda.org
Subject: Re: [IBIS-Users] (lv)pecl
Dear Fred,
Thank you for your reply. About the garbage; I explained it in an email I just sent (directed to Tom).
The s2ibis program does not generate IV- tables from 0-2.2V, but the program that has been modified by my collegue does do this (apart from the "garbage" that both programs produce).
Is this range enough? According to Tom it should be -3.3-6.6V. Where is this range for ECL/PECL defined? I cannot find it in the specification.
When the voltage is out of the normal operating range the currents can be very high, even so high that the transistor models are not valid anymore. What is the use of specifying these currents? Can they be left out? If not, what is done with this information.
I have the same question for the clamp currents. The output can be disabled, so this is a kind of tri-state (not really high impedant). Also here the currents are unrealistically high. What is done with this information? Why must it be specified? The PECL voltage swing is such that even a fully reflected signal will not cause the output to be outside the supply range.
With kind regards,
Ir. Erik van der Ven
Room DB1032
Business Line Networking Infrastructure
Philips Semiconductors BV
Gerstweg 2
6534 AE Nijmegen
The Netherlands
Phone: +31-24-3534334
Fred Balistreri <fred@apsimtech.com>
Sent by:
fred@interjet.apsimtech.com
05/09/03 07:10 PM
To: Erik van der Ven/NYM/SC/PHILIPS@EMEA2
cc:
Subject: Re: [IBIS-Users] (lv)pecl
Classification:
Erik, you need to define what convention you are
using when you say voltage range. Remember that
for ECL and PECL both the pullup and pulldown
reference is the same. If the voltage range
you refer to is the IBIS Vtable then your
range is not correct. Under the IBIS conventions
for ECL or PECL type Vtable= Vcc - Vout.
This is true for both pullup/pulldown for PECL/ECL.
IBIS further explains that for ECL, PECL the
range should be VCC - 2.2 volts. Under the
IBIS rules then the range should always be
0 - 2.2 volts for both pullup and pulldown.
Note that 0 really means 3.3 at the output
for your case and 2.2 really means 1.1 at the
output.
I don't quite understand your problem. You state
garbage. It's probably not quite descriptive
enough to understand your issue. Although the
meaning is clear.
Best Regards,
erik.van.der.ven@philips.com wrote:
>
> Part 1.1Type: Plain Text (text/plain)
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