Scott,
Some subtle points here. Are you measuring the s4p or extracting an s4p
from a solver. Is the 1 mile cable coiled up so the test equipment has
probes inches apart or a mile apart. These are questions about the quality
(accuracy) of the s4p.
I will try to re-phrase the question. When making measurements or using a
solver (and a solver does measurement by probes in a simulation or 3-d
field solver, the measurement of a port at one end of the cable are made
relative to a terminal at that end of the terminal. Another way of saying
this is that each port is two terminals at the same end of the cable. What
I believe Michael is asking:
* What is the s element N+1 terminal in HSPICE hook up to?
* How can this be a single reference for the Ports at both ends of
the cable if they are 1 mile away?
* Does it matter what node in the simulation the N+1 terminal of the
s-element is connected to (in HSPICE, in other SPICE simulators)?
* If it is OK to hook up this N+1 terminal to Node 0 in HSPICE, how
do simulators that claim they have no absolute ground (Node 0) hook up
this N+1 terminal so they have a legal return path for each Port?
* How do suppliers who create s parameter data (measurement or
solver) expect EDA tools to hook up terminal N+1?
* There are people that claim that there is no current flowing
through terminal N+1 because the S-Parameter assumption for interconnect
is that the current flowing from the signal terminal of a port is equal to
the current flowing to the reference terminal of the port. If this is
true, then it should not matter which node should be connected to the N+1
terminal. Is this a valid argument?
Walter
Walter Katz
wkatz@xxxxxxxxxx <mailto:wkatz@xxxxxxxxxx>
978.461-0449 x 133
Mobile 303.335-6156
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Scott McMorrow
Sent: Monday, February 26, 2018 8:29 PM
To: IBIS-Interconnect (ibis-interconn@xxxxxxxxxxxxx)
<ibis-interconn@xxxxxxxxxxxxx>; IBIS-ATM (ibis-macro@xxxxxxxxxxxxx)
<ibis-macro@xxxxxxxxxxxxx>; michael.mirmak@xxxxxxxxx
Subject: [ibis-macro] Re: S-parameter thought experiment
Michael
Define "described". What is the purpose of the black box measurements?
Any 2-wire, 4-terminal black box can be modeled with a measured
s-parameter. The question regarding the purpose is important, as it helps
to define the measurement needed.
Assume, for example, two wires in Free space. We can measure them in 2
ways. We can use differential and common mode probing to create e black
box. Or we can create a virtual ground reference between the conductors,
one in each end and measure single ended s parameters.
In either case, the measurements are valid and identical. N ports are
required.
However, unless the two wires are placed inside a Faraday cage the
measurements will be noisy, since they include the electromagnetic
environment of the universe. Instead, we use shorter sections that we
measure, and then extrapolate then out to one mile long.
I have no comment regarding the bird.
Get Outlook for Android <https://aka.ms/ghei36>
From: Mirmak, Michael
Sent: Monday, February 26, 7:36 PM
Subject: [ibis-macro] S-parameter thought experiment
To: IBIS-Interconnect (ibis-interconn@xxxxxxxxxxxxx
<mailto:ibis-interconn@xxxxxxxxxxxxx> ), IBIS-ATM
(ibis-macro@xxxxxxxxxxxxx <mailto:ibis-macro@xxxxxxxxxxxxx> )
(apologies if you have heard something like this before - I have discussed
it privately in a couple of contexts)
Imagine that I have a physical interconnect, consisting of a differential
pair of wires not particularly strongly coupled to each other. I want to
model the interconnect using an S-parameter set of at least 4 (four)
ports: two inputs P &N and two outputs P' & N'.
The problem: the physical pair of wires is approximately one mile in
length from P & N to P' & N'.
My questions:
1) Can this structure be correctly and unambiguously described using
a circuit with N terminals and an N+1 reference terminal? If not, how
many additional terminals are required?
2) Does the current BIRD189 draft, as written, enable correct and
unambiguous description(s) of this structure?
3) Does BIRD158.7, as written, enable correct and unambiguous
description(s) of this structure?
Thank you!
- MM
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