Continuing this thought, since IBIS is a component measurement based
system, and since measurement are made at the pin of a component, and
since every measurement at an I/O pin is made between that pin and some
nearby reference pin, then all we need to do is define a method of
determining the reference signal_name for every I/O pin. The following
algorithm should work for all known existing IBIS models:
1. [Pin Mapping] tells the bus_label on each of the buffer rail
2. These bus_labels define the signal_name on each of the rail
3. If just one signal_name is on a Pin with Model_name GND, and the
values of the Pullup Reference, Power Clamp Reference, Ground Clamp
Reference, Pulldown Reference assigned that has that signal_name has a
value of 0.0V in the [Model], then a pin of that signal_name near the I/O
pin is the reference for the measurements at the I/O pin. Similarly, the
I/O buffer rail terminal with the reference signal_name at the I/O buffer
is the reference node for measurements at the I/O buffer. Similarly, the
supply pads at the die/package boundary near the I/O die pad are the
reference for measurements at the I/O die pad.
If this algorithm does not work for an I/O buffer (and I claim such a case
does not exist) then we can enhance IBIS by adding an option [I/O
Reference] section that has two columns. The first column is the Pin_name
of an I/O buffer, and the second column is the signal_name of the
reference for all measurements at the I/O buffer.
From: Walter Katz [mailto:wkatz@xxxxxxxxxx]
Sent: Saturday, February 27, 2016 8:58 PM
To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
Subject: One of the rail voltages of every IBIS buffer is a GND
signal_name and a reference node.
I have looked at the data sheets for parts with RS232, ECL, PECL and MECL
buffers, and every one of them has one of the rail voltages connected to a
Ground (GND) data book name (signal_name).
Although the IBIS standard does allow the user to associate all of the
rail voltages with bus_labels on POWER pins, such a buffer is an unnatural
If we state that it is a given that every buffer has a Ground rail
connection, then we can state that every buffer has a well-defined
reference node for every other terminal measurement at the buffer.
I challenge anyone on this committee to find a part with an I/O buffer
that has no rail terminals that are Ground.