[ibis-macro] What IEEE says about referencing

From: Walter Katz <wkatz@xxxxxxxxxx>
To: "'IBIS-Interconnect'" <ibis-interconn@xxxxxxxxxxxxx>, "IBIS-ATM" <ibis-macro@xxxxxxxxxxxxx>, "'IBIS-Editorial'" <ibis-editorial@xxxxxxxxxxxxx>
Date: Tue, 19 Jul 2016 10:06:43 -0400 (EDT)

All,

What S Parameter experts say about Port Referencing. The following is from
a proposed section of the IEEE P370 working group on measurement quality
of S parameters. Note the sentence highlighted in red. To me, this says
that the "reference" or more importantly the return flow terminals of I/O
terminals of package interconnect at the pin interface should connect to
the corresponding I/O terminals and return flow terminals of the PCB
interconnect.

So if a wline is referenced to VSS inside of the package, then the wlines
it connects to on the PCB should also be referenced to VSS on the board.

This is obviously a rule that IBIS cannot inforce on package and die
interconnect models at the Pin, Die Pad or Buffer interface, and we must
rely on the model maker, and the PCB designer to get that right.

Walter

7.3 Definitions

7.3.1 Network Parameters in General

This chapter briefly describes the theory of multiports in general and
scattering parameters (S-parameters) descriptors of multiports in
particular.

Multiport is a natural and scalable black-box description of linear
time-invariant system. It reduces a system description to a simple
input-output relationship irrespective of possible complicated internal
structure. It is suitable for systems smaller that, comparable with or
larger than wavelength (literally DC to daylight and beyond). Any
interconnect or wave-guiding structure can be described as a multiport
with possible inclusion of radiation. In general, multiport theory
facilitates description of a complex interconnect system of any type - PCB
and packaging traces, fiber optics, waveguides and so on.

A multiport or N-port with equivalent currents and voltages is shown in
Fig. 7.3.1.1 according to the classic circuit theory definition [7.3.1.1]
- [7.3.1.3].

Fig. 7.3.1.1. Multiport currents and voltages definition.

Ports are numbered from 1 to N. Each port has two terminals. One terminal
is the signal and another terminal is local reference or local ground
terminal. Current flowing in the signal terminal is equal to current
flowing out of the reference terminal at each port. Connection of
multiports requires that the definition of the terminals on both sides of
the connection is the same. It means that the local references can be
different for different ports of a multiport, but they have to coincide
with the local reference terminals of another multiport to be connected.
Some groups of ports may share the reference terminals. The currents and
voltages at ports are either actual measurable values or effective
voltages and currents as in microwave theory. In frequency domain, the
currents and voltages are complex variables and can be united into vectors
with N complex elements:

Walter Katz

<mailto:wkatz@xxxxxxxxxx> wkatz@xxxxxxxxxx

Phone 303.449-2308

Mobile 303.335-6156

Follow-Ups:
- [ibis-macro] Re: [ibis-interconn] What IEEE says about referencing
  - From: Bradley Brim

[ibis-macro] What IEEE says about referencing

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