Subject: RE: [IBIS-Users] Re: [IBIS] BIRD82 - Clarification of Clamp Table Use
From: Angulo, John (john_angulo@mentorg.com)
Date: Fri Jul 11 2003 - 11:08:59 PDT
If I understand, then, one source of double counting is that people sometimes put both diode curves into each clamp table because they're worried that only one clamp table actually will be used - [GND Clamp] in the low state, [POWER Clamp] in the high state. Clarifying that both clamp tables are always present will prevent this.
I also may have seen a model or two that double counted the currents because the model maker didn't realize the tables were added as parallel electrical elements. He or she thought that the tables would be "added" by concatenation to form a bigger table containing the currents of both tables and spanning their combined voltage range. Not so, of course - if the buffer contains an internal pullup resistor, and the current through that resistor appears in both tables, it will be double counted, both by EDA tools and the committee parser. At least the I-V/V-T mismatch check will detect the problem if V-T tables are present. I wonder if this is worth an additional clarifying comment in the BIRD.
John Angulo
Hyperlynx Products
Mentor Graphics Corp.
john_angulo@mentor.com
425-869-2320
-----Original Message-----
From: Todd Westerhoff [mailto:twesterh@cisco.com]
Sent: Friday, July 11, 2003 7:42 AM
To: ibis@eda.org
Subject: RE: [IBIS-Users] Re: [IBIS] BIRD82 - Clarification of Clamp Table Use
I agree. I believe both clamp curves are summed together with the driving device's V-I curve.
However, in all matters of Algorithms, I defer to Arpad.
Todd ;-)
Todd Westerhoff
High Speed Design Specialist
Cisco Systems
1414 Massachusetts Ave - Boxboro, MA - 01719
email:twesterh@cisco.com
ph: 978-936-2149
============================================
"When did the choices get so hard, with so much more at stake?
Life gets mighty precious when there's less of it to waste"
- Bonnie Raitt, "Nick of Time"
-----Original Message-----
From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org]On Behalf Of rob.mataheroe@philips.com
Sent: Friday, July 11, 2003 4:40 AM
To: Mirmak, Michael
Cc: ibis@eda.org; ibis-users@eda.org; owner-ibis@eda.org
Subject: [IBIS-Users] Re: [IBIS] BIRD82 - Clarification of Clamp Table Use
:Michael,
Isn't there a typing error in the proposed text? In my opinion both clamp tables should be summed to the Pullup table when the buffer is driving high.
| It is assumed that the simulator will sum both clamp tables
| (power and ground), if they exist, to the Pullup table when
| the buffer is driving high.
Kind regards,
Rob
__________________________________________________________________________
Rob Mataheroe Philips Semiconductors bv
P.G. Logic Product Group PD&S Building AM1.108
Senior Design Modeling Engineer Gerstweg 2
Tel. ++31 (0)24 353 2370 6534 AE Nijmegen
Fax. ++31 (0)24 353 2820 The Netherlands
Telework: 036-5225406 (From PS Nijm.: **0731)
Email: Rob.Mataheroe@philips.com
Seri: matahero@nyhp04
"Mirmak, Michael" <michael.mirmak@intel.com>
Sent by:
owner-ibis@eda.org
07/11/03 06:19 AM
To: <ibis@eda.org>
<ibis-users@eda.org>
cc: (bcc: Rob Mataheroe/NYM/SC/PHILIPS)
Subject: [IBIS] BIRD82 - Clarification of Clamp Table Use
Classification:
The following BIRD is posted on behalf of Lynne Green and Robert Haller.
It will be discussed at the July 18, 2003 IBIS Open Forum
teleconference.
- Michael Mirmak
Intel Corp.
Chair, EIA/IBIS Open Forum
************************************************************************
****
************************************************************************
****
Buffer Issue Resolution Document (BIRD)
BIRD ID#: 82
ISSUE TITLE: Clarification of Clamp Table Use
REQUESTOR: Lynne Green, Cadence, and Robert Haller, SiSoft
DATE SUBMITTED: June 27, 2003
DATE ACCEPTED BY IBIS OPEN FORUM: Pending
************************************************************************
****
************************************************************************
****
STATEMENT OF THE ISSUE:
Double-counting of clamp currents is the result of confusion over how
the
clamp currents are summed by the tools. Model makers are often unsure
if
clamps are always active, or whether the [Power Clamp] works only with
the
[Pullup] and the [GND Clamp] only with the [Pulldown]. This is
difficult,
if not impossible, to detect with a parser.
************************************************************************
****
STATEMENT OF THE RESOLVED SPECIFICATIONS:
Old text:
| It is assumed that the simulator sums the clamp tables
| together with the appropriate [Pullup] or [Pulldown] table
| when a buffer is driving high or low, respectively. From this
| assumption and the nature of 3-statable buffers, it follows
| that the data in the clamping table sections are handled as
| constantly present tables and the [Pullup] and [Pulldown]
| tables are used only when needed in the simulation.
Proposed text:
| It is assumed that the simulator will sum both clamp tables
| (power and ground), if they exist, to the Pulldown table when
| the buffer is driving high. The simulator will sum both clamp
| tables (power and ground), if they exist, to the Pulldown
table
| when the buffer is driving low. The simulator will sum both
| clamp tables when the buffer is not driving (input or 3-state
| operation).
| It follows that the data in the clamping table sections are
| handled as constantly present tables, while the [Pullup] and
| [Pulldown] tables are used only when needed in the simulation.
************************************************************************
****
ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:
Comments from members of the Quality committee, as well as others,
indicated that some models double-count clamp currents.
************************************************************************
****
ANY OTHER BACKGROUND INFORMATION:
Initially, it was suggested that this be detected by the parser, but
it was decided that this was too difficult. This led to further
discussion of why double-counting occurred, and how clarification of
the spec could help address the issue.
************************************************************************
****
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