All,
If we choose to include BIRD 189 and not BIRD 181 in IBIS 7.0 we could
include the following (either in a BIRD, or in a statement that accompanies
IBIS 7.0). The following is a firm grasp of the obvious. It is technically
correct.
In IBIS 6.1 and all previous revisions of IBIS, the I/O buffer terminals
where assumed to be at the die pads (die package interface). The on-die
interconnect between the die pad and the buffer terminals has always been
assumed to be included in the IBIS I/O buffer model, either in the IV curves
and/or in C_comp. At the high data rates of modern I/O buffers this is no
longer sufficiently accurate. BIRD 189 addresses this by allowing the
package interconnect model to be defined either between the pins of the
component and the I/O buffer signal and rail terminals, or to be split
between the pins of the component and terminals at the die-pad/package
interface and between the die-pad/package interface and the I/O buffer
terminals.
BIRD 189 package models that are defined between the pins and the I/O buffer
terminal models may or may not include the interconnect between the die-pads
and the I/O buffer terminals. If the package models do not include on-die
interconnect, then I/O buffer models need to be constructed as before, and
include the on-die interconnect in their IV curves and/or C_comp. If the
package models do include on-die interconnect, then I/O buffer models need
to be constructed (most likely through a SPICE-to-IBIS or similar process),
and not include the on-die parasitics that are included in the package
models.
There are many places in the current IBIS specification (6.1) that name the
I/O buffer terminals. These names did not anticipate the requirement that
these terminals could either be at the die-pad package interface, or
internal to the die and not at the die-pad interface. EDA tools shall assume
that all IBIS data is defined at the I/O buffer terminals, and that these
terminals are connected to BIRD 189 "Buf" terminals, and that there is no
double counting of on-die interconnect included in the I/O Buffer model and
the package interconnect.
Using legacy package models that assume the on-die interconnect is included
in the I/O buffer models when BIRD 189 package models will leave out any
on-die interconnect that is included in the BIRD 189 package models.
Walter
Walter Katz
wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 303.335-6156
