All,
I suspect that there will be an IBIS 6.2 which will be strictly limited to
cleaning up Ground in IBIS. I put the following together as an
introduction to this "BIRD". I do not know how this would be parsed into
the IBIS document, but I wanted to first get an agreement as to the intent
of the change, before going through IBIS to actually wordsmith the
changes. I propose that we get agreement on this within IBIS-ATM, and then
charter an editorial committee to go through IBIS 6.1, make all of the
changes, and then submit the edited document to IBIS for approval as IBIS
6.2.
GND, Ground, Reference Node, Node 0, A_gnd and Absolute Ground need
carefull review and documentation. When IBIS was originally written
"Ground" was often interpreted to be truly global, have a value of 0.0
Volts and represented as Node 0 in SPICE simulators. The name GND is
actually used in several different contexts in this document.
* In General Syntax Rule 2, "GND - reserved model
name, used with ground pins" is only limited to the use of GND in the
Model_name column of records in the [Pin] section of [Components].
* GND is often used in the context of Signal_name in [Pin]
examples. The Signal_name GND in this context is the Data Book name of the
Pin.
* IV tables define the current contribution to the A_signal node
of an I/O buffer model. The voltage used to control these tables is the
voltage between the A_signal node of an I/O buffer and the pullup,
pulldown, ground or power rail voltage at the buffer. This should not be
confused with the derivation method used to create the data in the IV
tables which refer to GND, Ground, Absolute Ground, or static voltages
reference to test fixture ground. The use of the node name GND, the ground
symbol ---, or names such as GND_Clamp_Reference, Power_Clamp_Reference,
Pullup_Reference, Pulldown_Reference are voltages relative to the Test
Fixture Ground.
SPICE (including AMS language) signal integrity simulations are preformed
using netlists of connected interconnect models, power delivery models,
I/O buffer models, and simulator dependent control elements. The IBIS
organization defines standards for distributing interconnect models and
I/O buffer models. Ultimately these models are instantiated in simulation
netlists as instances of SPICE elements that have terminals. Terminals
that have the same name are "connected" and have the same voltage
potential, and are called a node. The operation of any interconnect model
or I/O buffer models is a function of the voltage potential difference
between the nodes of the terminals of that model. A simulator may (and
usually does) have a concept of a reference node (often referred to as
Node 0, Absolute Ground, or GND), the I/O buffer or interconnect elements
should not use this node and certainly should not supply current to or
draw current from this internal simulator reference node. This node 0
should not be confused with the use of the name GND in this IBIS document.
Walter
Walter Katz
<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx
Phone 303.449-2308
Mobile 303.335-6156
