Subject: Can't do T-LINE?

From: Chris Rokusek <[email-masked]>
Date: Tue, 19 May 1998 17:56:15 -0700

( I am reposting this question in hopes of a more helpful response )

Hi All,

Concerning [Path Description] section in Ver 3.x of .ibs...

The 'len' parameter is given in 'units' which is 'arbitrary' (i.e. not
meters) such that a distributed T-LINE model cannot be built with the
proper physical length.

** I DO NOT WANT TO BUILD A LUMPED MODEL, I WANT TO BUILD A T-LINE MODEL
**

Is this an oversight or am I not understanding the parameters?

Best Regards,

Chris Rokusek
Viewlogic Systems

|============================================================================= 
|     Keyword:  [Path Description]
|    Required:  Yes
| Description:  This keyword allows the user to describe the connection
|               between the user accessible pins of a part and the pins
of the 
|               ICs mounted on that part.  Each pin to node connection
is
|               divided into one or more cascaded "sections", where each
|               section is described in terms of it's L/R/C per unit
length.
|               The Fork and Endfork subparameters allow the path to
branch to 
|               multiple nodes, or another pin.  A path description is
|               required for each pin whose signal name is not "GND",
"POWER" 
|               or "NC".
|
|               Board Description and IC Boundaries: 
|
|               In any system, each part interfaces with another part at
some 
|               boundary.  Every part model must contain the components 
|               necessary to represent the behavior of the part being
modeled 
|               within its boundaries. The boundary definition depends
upon 
|               the parts being represented by the model. 
|
|               For CARD EDGE CONNECTIONS such as a SIMM or a PC
Daughter 
|               Card plugged into a SIMM Socket or Edge Connector, the 
|               boundary should be at the end of the board card edge
pads as 
|               they emerge from the connector.
|
|               For any THROUGH-HOLE MOUNTED PART, the boundary will be
at the 
|               surface of the board on which the part is mounted.
|
|               SURFACE MOUNTED PART models end at the outboard end of
their 
|               recommended surface mount pads.
|
|               If the board level component contains an UNMATED
CONNECTOR, 
|               the unmated connector will be described in a separate
file, 
|               with its boundaries being as described above for the
|               through-hole or surface mounted part. 
|
|  Sub-Params:  Len, L, R, C, Fork, Endfork, Pin, Node
| Usage Rules:  Each individual connection path (user pin to node(s))
|               description begins with the [Path Description] keyword
and a 
|               path name, followed by the subparameters used to
describe the 
|               path topology and the electrical characteristics of each
|               section of the path.  The path name must not exceed 40
|               characters, blanks are not allowed, and each occurrence
of the 
|               [Path Description] keyword must be followed by a unique
path
|               name.  Every signal pin (pins other than POWER, GND or
NC) 
|               must appear in one and only one path description per
[Begin
|               Board Description]/[End Board Description] pair.  Pin
names do 
|               not have to appear in the same order as listed in the
[Pin
|               List] table.  The individual subparameters are broken up
into 
|               those that describe the electrical properties of a
section,
|               and those that describe the topology of a path. 
|
|               Section Description Subparameters: 
|
|               The Len, L, R, and C subparameters specify the length,
the
|               series inductance and resistance and the capacitance to
ground 
|               of each section in a path description.
|
|               Len     The physical length of a section.  Lengths are
given 
|                       in terms of arbitrary 'units'.  Any non-zero
length 
|                       requires that the parameters that follow must be
|                       interpreted as distributed elements by the
simulator. 
|               L       The series inductance of a section, in terms of
|                       'inductance/unit length'.  For example, if the
total 
|                       inductance of a section is 3.0 nH and the length
of 
|                       the section is 2 'units', the inductance would
be
|                       listed as L = 1.5 nH  (i.e. 3.0 / 2). 
|               C       The capacitance to ground of a section, in terms
of 
|                       capacitance per unit length.
|               R       The series DC (ohmic) resistance of a section,
in 
|                       terms of ohms per unit length.
|
|               Topology Description Subparameters: 
|
|               The Fork and Endfork subparameters denote branches from
the 
|               main pin-to-node or pin-to-pin connection path.  The
Node 
|               subparameter is used to reference the pin of a component
or
|               board as defined in a .ibs or .ebd file.  The Pin
subparameter 
|               is used to indicate the point at which a path connects
to a
|               user visible pin.
| 
|               Fork    This subparameter indicates that the sections
|                       following (up to the Endfork subparameter) are
part 
|                       of a branch off of the main connection path. 
This 
|                       subparameter has no arguments.
|               Endfork This subparameter indicates the end point of a
branch. 
|                       For every Fork subparameter there must be a
|                       corresponding Endfork subparameter.  As with the
Fork 
|                       subparameter, the Endfork subparameter has no
|                       arguments.
|               Node    reference_designator.pin
|                       This subparameter is used when the connection
path
|                       connects to a pin of another, externally defined
part. 
|                       The arguments of the Node subparameter indicate
the
|                       pin and reference designator of the external
|                       component.  The pin and reference designator
portions 
|                       of the argument are separated by a period
(".").  The 
|                       reference designator is mapped to an external
|                       component description (another .ebd file or .ibs
file) 
|                       by the [Reference Designator Map] Keyword.  Note
that 
|                       a Node MUST reference a model of a passive or
active
|                       component.  A Node is not an arbitrary
connection 
|                       point between two elements or paths.
|               Pin     This subparameter is used to mark the point at
which 
|                       a path description connects to a user accessible
pin. 
|                       Every path description must contain at least one 
|                       occurrence of the Pin subparameter.  It may also
|                       contain the reserved word NC.  The value of the
Pin 
|                       subparameter must be one of the pin names listed
in 
|                       the [Pin List] section.
|
|               Using The Subparameters to Describe Paths: 
|
|               A section description begins with the Len subparameter
and
|               ends with the slash (/) character.  The value of the
Len, L, 
|               R, and C subparameters and the subparameter itself are
|               separated by an equals sign (=); whitespace around the
equals 
|               sign is optional.  The Fork, Endfork, Node and Pin
|               subparameters are placed between section descriptions
(i.e., 
|               between the concluding slash of one section and the
'Len'
|               parameters that starts another).  The arguments of the
Pin and 
|               Node subparameter are separated by white space. 
|
|               Specifying a Len or L/R/C value of zero is allowed.  If
|               Len = 0 is specified, then the L/R/C values are the
total for 
|               that section.  If a non-zero length is specified, then
the
|               total L/R/C for a section is calculated by multiplying
the
|               value of the Len subparameter by the value of the L, R,
or C 
|               subparameter.  However, as noted below, if a non-zero
length 
|               is specified, that section MUST be interpreted as
distributed 
|               elements.
|
|               Legal Subparameter Combinations for Section
Descriptions: 
|
|               A)  Len, and one or more of the L, R and C
subparameters.  If 
|               the Len subparameter is given as zero, then the L/R/C
|               subparameters represent lumped elements.  If the Len
|               subparameter is non-zero, then the L/R/C subparameters 
|               represent distributed elements and both L and C must be 
|               specified, R is optional.
|
|               B) The first subparameter following the [Path
Description] 
|               keyword must be 'Pin', followed by one or more section
|               descriptions.  The path description can terminate in a
Node, 
|               another pin or the reserved word, NC.
|
|               Dealing With Series Elements: 
|
|               A discrete series R or L component can be included in a
path
|               description by defining a section with L=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] with a series component is
not 
|               allowed.
|----------------------------------------------------------------------------- 
|
|  An Example Path For a SIMM Module: 
|
[Path Description] CAS_2
Pin J25
Len = 0.5 L=8.35n C=3.34p R=0.01 /
Node u21.15
Len = 0.5 L=8.35n C=3.34p R=0.01 /
Node u22.15
Len = 0.5 L=8.35n C=3.34p R=0.01 /
Node u23.15
|
|  A Description Using The Fork and Endfork Subparameters: 
|
[Path Description] PassThru1
Pin B5
Len = 0   L=2.0n /
Len = 2.1 L=6.0n C=2.0p /
 Fork
 Len = 1.0 L = 1.0n C= 2.0p /
 Node u23.15
 Endfork
Len = 1.0 L = 6.0n C=2.0p /
Pin A5
|
|  A Description Including a Discrete Series Element: 
|
[Path Description] sig1
Pin B27
Len = 0  L=1.6n /
Len = 1.5 L=6.0n C=2.0p /
Node R2.1
Node R2.2
Len = 0.25 L=6.0n C=2.0p /
Node U25.6
|
|=============================================================================

---

From: [email-masked] (Bob Ross)
Date: Tue, 19 May 98 19:03:38 PDT

Chris:

The L, C, and R parameters are given as CORRESPONDING per unit length values.
These are multiplied by Len to produce the total distributed values for the
exact length of T-line that you want.

Whenever Len is not equal to zero, the section is interpreted as
a distributed section (not a lumped section).

The T-line relationships still hold:

   Zo = sqrt(L/C)
   TD = Len * sqrt(LC)

So the electrical information is available for a T-line of whatever length
you want.

Best Regards,
Bob Ross
Interconnectix/Mentor Graphics

> Sender: [email-masked]
> Date: Tue, 19 May 1998 17:56:15 -0700
> From: Chris Rokusek <[email-masked]>
> To: [email-masked]
> Subject: Can't do T-LINE?

---

From: Kellee Crisafulli <[email-masked]>
Date: Tue, 19 May 1998 20:40:02 -0700

Hi Chris,

 This is not an oversight and you can and should build
a distributed model if both L and C are present and it has
non-zero length it is suppose to be a distributed model.
Z0 = sqrt(L/C)
delay = sqrt(L*C)
The key is that the L and C are per unit length.
as is stated in the text.  Just multiply the delay times
the length specified.

---

From: Andrew Ingraham <[email-masked]>
Date: Wed, 20 May 1998 07:35:20 -0400

> meters) such that a distributed T-LINE model cannot be built with the

The 'len' parameter is in arbitrary 'units' which allows you to use
meters, while someone else could use mm, inches, feet, or whatever ...
as long as they are consistent with the rest of the t-line parameters,
L/R/C.

Regards,
Andy