Buffer Issue Resolution Document  (BIRD)

BIRD ID#:        111
ISSUE TITLE:     Extended Usage of External Series Components in EBDs
REQUESTOR:       Michael Schaeder, Zuken
DATE SUBMITTED:  July 1, 2008
DATE REVISED:                       
DATE ACCEPTED BY IBIS OPEN FORUM: Pending

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STATEMENT OF THE ISSUE:

The current EBD specification states that discrete Series Components can be
defined by writing two back to back node statements that reference the same
component. In this case, both ends of the discrete two terminal component must
be contained in a single path description. Connecting two separate path
descriptions with a series component is not allowed.

However, many EBDs available in industry also use external Series Components
in EBDs that connect two separate paths, mainly to define differential
termination resistors. Such EBDs also pass the IBIS Golden Parser without any
problem.

Therefore the current EBD specification should be modified such that it is
allowed to insert Series Components between two branches of a single path
description or between two separate path descriptions.


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STATEMENT OF THE RESOLVED SPECIFICATIONS:

Changes are noted in the relevant sections below by |* lines.

Replace the following text of the  "Dealing With Series Elements" paragraph
of the [Path Description] keyword in section 8 (from the 4.2/5.0a spec):

|               A discrete series R or L component can be included in a path
|               description by defining a section with Len=0 and the proper R
|               or L value.  A discrete series component can also be included
|               in a path description by writing two back to back node
|               statements that reference the same component (see the example
|               below).  Note that both ends of a discrete, two terminal
|               component MUST be contained in a single [Path Description].
|               Connecting two separate [Path Description]s with a series
|               component is not allowed.

with:

|               A discrete series R or L component can be included in a path
|               description by defining a section with Len=0 and the proper R
|               or L value.  A discrete series component can also be included
|*              by writing node statements that reference the same component.
|*              This can be done as two back to back node statements for a
|*              series component within a single [Path Description]. It is
|*              also allowed to insert a series component between two branches
|*              of a single [Path Description], or even between two separate
|*              [Path Description]s (see the examples below).

Add the following examples:

| a path including series passive components (C17, R21)
| between branches forming a differential termination
| 
|
[Path Description]   CLK
Pin 137
Node C17.1
 Fork
  R21.1
  R21.2
 Endfork
Node C17.2
Pin 138
|
|        +-------------------------------------------------------------
|        |
|   137 <--------+--------+
|        |       |        |
|        |    +--+--+  +--+--+
|        |    |Pin 1|  |Pin 1|
|        |    |     |  |     |
|        |    | C17 |  | R21 |
|        |    |     |  |     |
|        |    |Pin 2|  |Pin 2|
|        |    +--+--+  +--+--+
|        |       |        |
|   138 <--------+--------+
|        |
|
|
| two paths connected by series resistors (R8, R9) used as
|  differntial termination between components
|
[Path Description] DP+
Pin 20
Fork
 Fork
  D7.P8
 Endfork
 R8.1
Endfork
Fork
 D5.P8
Endfork
R9.1

[...]

[Path Description] DP-
Pin 22
Fork
 Fork
  D7.Q8
 Endfork
 R8.2
Endfork
Fork
 D5.Q8
Endfork
R9.2
|
|
|        +-------------------------------------------------------------
|        |                                   +------+
|        |                                   |Pin   |
|    20 <---------+--------------------+-----+P8  D7|
|        |        |                    |     |      |
|        |        |     +------+       |     +------+
|        |        |     |Pin   |       |   
|        |        +-----+P8  D5|       |   
|        |        |     |      |       |   
|        |     +--+--+  +------+    +--+--+
|        |     |Pin 1|              |Pin 1|
|        |     |     |              |     |
|        |     |  R9 |              |  R8 |
|        |        .                    .
|        |        .                    .
|        |        .                    .
|        |                       
|        |     |  R9 |              |  R8 |
|        |     |     |              |     |
|        |     |Pin 2|              |Pin 2|
|        |     +--+--+  +------+    +--+--+
|        |        |     |Pin   |       |
|        |        +-----+Q8  D5|       |
|        |        |     |      |       |
|        |        |     +------+       |     +------+
|        |        |                    |     |Pin   |
|     22<---------+--------------------+-----+Q8  D7|
|        |                                   |      |
|        |                                   +------+
|
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ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:

Today there are some EBD models available that use series components
connecting separate path descriptions in the way it is outlined above.
Typical applications areas are DIMM modules and diferential termination
networks.  Since this usage of EBD description capabilities is required
to enable these kinds of modeling the IBIS Standard should be updated
to reflect it's usage in the industry.

The new definition outlined above is most suitable to define differential 
pair termination in the most flexible way.

As the IBIS Golden Parser already accepts this EBD syntax it need not to
be changed.  Applications need to be extended in order to consider series
components used this way.

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ANY OTHER BACKGROUND INFORMATION:


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