Subject: [IBIS] BIRD82 - Clarification of Clamp Table Use CORRECTED
From: Mirmak, Michael (michael.mirmak@intel.com)
Date: Fri Jul 11 2003 - 11:57:15 PDT
An early draft of BIRD82 was accidentally posted yesterday. The correct
version is enclosed.
- Michael Mirmak
Intel Corp.
Chair, EIA/IBIS Open Forum
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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
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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.
This issue can be resolved by clarification of the text under
| Keywords: [Pulldown], [Pullup], [GND Clamp], [POWER Clamp]
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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 [Pullup] 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 effects, while the [Pullup] and
| [Pulldown] tables are used only when needed in the simulation.
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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.
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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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