Subject: Re: [IBIS-Users] input thresholds for ECL model
From: Ingraham, Andrew (a.ingraham@ieee.org)
Date: Tue Nov 18 2003 - 06:55:32 PST
But the interesting thing is when you consider that you can use the same component for either ECL or PECL. It's just a question of how you hook it up.
It might have been considered "undesirable" (in certain circumstances) to use an "ECL" part with Vee as ground reference and a positive Vcc supply voltage, but there really isn't anything stopping you from doing it if you control the Vcc noise across the system. Likewise for a "PECL" part on a negative supply voltage, but that would be more likely. These days most multilayer boards use power planes as well as ground planes, so there isn't really much of a valid reason to think that "ground" is especially quieter than "power" is.
Back several years ago when IBIS was made ECL-aware, I suspect most ECL used a negative supply. Hence the negative numbers that are seen in the spec.
IBIS models define which pins are connected to GND and which to POWER, although I don't know what, if anything, a sim. tool does with those keywords. All voltages are referenced to GND and those pins connected to it. An intelligent tool might have noticed when the user connects the IC's GND pins to a positive or negative supply voltage, and adjust things accordingly. (In retrospect, perhaps it would have been better to have avoided any references to GND in the IBIS Spec. GND is a system feature and is really out of context for an IC ... everything on an IC is relative. That was one of the things that bothered me when I first read the IBIS spec, a decade ago, and still bothers me.)
If you have a component that you think might be used either way (ECL or PECL), you could construct one model for use with a positive supply and another for a negative supply. They would have different pin mappings and voltage values (including Vinh, Vinl, Vmeas, Vref) according to intended use.
Regards,
Andy
----- Original Message -----
From: Tom Dagostino
To: erik.van.der.ven@philips.com ; ibis-users@eda.org
Cc: john_angulo@mentorg.com
Sent: Tuesday, November 18, 2003 03:32 AM
Subject: RE: [IBIS-Users] input thresholds for ECL model
Eric
The threshold voltages for any buffer are the absolute voltage for Vinl and Vinh. Thus for ECL you would see negative numbers and for PECL you would have positive numbers. For example, from the ON 100lve111 PECL operation Vinh would be 2.42V and Vinl would be1.49V. For ECL operation Vinh would be -0.880 and Vinl would be -1.810.
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 erik.van.der.ven@philips.com
Sent: Tuesday, November 18, 2003 12:15 AM
To: ibis-users@eda.org
Cc: john_angulo@mentorg.com
Subject: [IBIS-Users] input thresholds for ECL model
This posting was not well received last time, so I post it again.
With kind regards,
Ir. Erik van der Ven
Room DB1029
Business Line Networking Infrastructure
Philips Semiconductors BV
Gerstweg 2
6534 AE Nijmegen
The Netherlands
Phone: +31-24-3534334
----- Forwarded by Erik van der Ven/NYM/SC/PHILIPS on 11/18/03 09:15 AM -----
Erik van der Ven
11/10/03 10:17 AM
To: ibis-users@eda.org
cc:
Subject: input thresholds for ECL model
Classification: Unclassified
Dear IBIS users,
I am modeling an LVPECL input buffer, using the input_ecl model.
How are the Vinl and Vinh defined?
In the 3.2 buffer spec I see an example of negative values. Are these referenced to supply voltage?
I cannot find the definition. Can someone tell me where to find it?
I looked at some buffer models of other's, and found that they use positive values.
With kind regards,
Erik.
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
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