ICM Issue Resolution Document  (IIRD)

IIRD ID#:        7
ISSUE TITLE:     Clarification of Off-Diagonal Matrix Terms
REQUESTOR:       Michael Mirmak, Intel Corporation
DATE SUBMITTED:  September 10, 2004
DATE REVISED:    
DATE ACCEPTED BY IBIS OPEN FORUM: 

****************************************************************************
****************************************************************************

STATEMENT OF THE ISSUE:

The language used in the ICM 1.0 specification to describe [Resistance Matrix] 
data does not clearly establish the meaning of off-diagonal terms, especially
for missing Sparse_matrix columns or where the matrix is not present.

Much of the specification language used to describe "Diagonal_matrix," "Banded_matrix"
formats, etc. involves the phrase "entries are guaranteed to be zero if they
are not on the main diagonal."  This implies that the resistance matrix
off-diagonal elements are to be interpreted as many leading tools actually do 
interpret them, namely as a relationship between the current on one conductor 
and the voltage on another.  A value of zero implies "no relationship."

However, language specific to the [Resistance Matrix] definition states that off-diagonals
are to be assumed "infinite."  This suggests that the off-diagonals describe
a real resistive connection between conductors.  Few, if any, industry
field solvers present off-diagonal resistance matrix data in this form.

Finally, the sign convention for mutual resistances is described as important
in one part of the specification, but the allowed number formats for
[Resistance Matrix] data later in the text is omitted, unlike the descriptions 
of the other matrix formats.

IIRD7 attempts to clarify the issue, by explicitly stating that off-diagonal
[Resistance Matrix] data refers explicitly to the relationship between
currents on one conductor and voltages on another, implying zero off-diagonal
values as defaults.  IIRD7 also adds language to explictly state that missing
matrix data for any matrix is assumed equal to 0.0


****************************************************************************

STATEMENT OF THE RESOLVED SPECIFICATIONS:

Changes in IIRD7 are denoted by |*.
 
The text of Section 8, under the definition of the [Resistance Matrix], etc.,
should be changed as follows:

Remove the following sentence:
|* Users should be aware that matrix data of value 0 represents an 
|* ideal short to reference ground and should not be associated 
|* with conductors which carry signal information (see below).

and replace it with:
|* For all matrix keyword data sets below, both diagonal and non-diagonal 
|* entries are assumed to contain actual values of resistance, conductance, 
|* etc.  For example, a [Resistance Matrix] is assumed to contain information 
|* in the form of ohms or ohms per unit length, depending on the use of the 
|* Mult or Len modifiers.  

|* Values for non-listed [Row] or column entries or for matrices not explicitly 
|* defined shall be assumed equal to 0.0.

----------------------------------------------------------------------

Under "Resistance Matrix Description," remove the following:
|* The resistance matrix is optional.  Simulation tools shall use
|* 0.0 ohms for all diagonal entries and "infinite" for all off-
|* diagonal entries if this matrix is not present.

and replace it with:
|* The resistance matrix is optional.  

|* Users and model authors should be aware that [Resistance Matrix] data of 
|* value 0 in the diagonal represents an ideal short. 

|* Note that a value of 0 ohms in the off-diagonal of a [Resistance Matrix] 
|* does NOT imply a short circuit between conductors.  The off diagonal entries 
|* in resistance matrices relate the voltage generated in one conductor to a 
|* current in another. Using Ohm's law (V=I*R), an off-diagonal resistance 
|* value of zero indicates the absence of resistive coupling between the conductors.

----------------------------------------------------------------------

Also under "Resistance Matrix Description," remove the following:
|* Diagonal elements may be dominant.  Comparably, the off-diagonal elements
|* may be negligible thus leading to off-diagonal element values of infinite value.
|* Therefore, a "Diagonal_matrix" matrix type is the best choice for describing
|* a resistance matrix.

and replace it with:
|* In many cases, diagonal elements may be dominant and off-diagonal elements
|* (expressing the relationship between the current on one conductor and the voltage 
|* on the other) may be negligible.  Therefore, a "Diagonal_matrix" matrix type is 
|* usually the best choice for describing a resistance matrix.  Off-diagonal
|* terms, when other matrix types are used, may be positive real numbers, negative
|* real numbers or zero.


****************************************************************************

ANALYSIS PATH/DATA THAT LED TO SPECIFICATION:

The changes above were discovered as a result of an IBIS Futures Committee
discussion of IIRD 2.2.  The language above on off-diagonal [Resistance Matrix]
data is paraphrased from excellent SI-LIST discussions in February 2003 and from
comments by Bob Ross and Arpad Muranyi.

****************************************************************************

ANY OTHER BACKGROUND INFORMATION:


****************************************************************************