[ibis-interconn] Re: Touchstone Interconnect Causality, Passivity and Symmetry
- From: Bob Ross <bob@xxxxxxxxxxxxx>
- To: "Dmitriev-Zdorov, Vladimir" <vladimir_dmitriev-zdorov@xxxxxxxxxx>
- Date: Thu, 14 Jan 2010 09:54:13 -0800
All:
As a brief note, Yuriy Shlepnev of Simberian will expand on these
topics in a presentation "Quality Metrics for S-parameter Models"
at the IBIS Summit at DesignCon.
Bob
Dmitriev-Zdorov, Vladimir wrote:
Walter,
There is no rule that says an interconnect Touchstone file is
symmetric. It is only symmetric if the interconnect is symmetric.
We should distinguish between matrix symmetry and structural symmetry of
the interconnect.
The first does not require anything except reciprocity. Any circuit
composed from linear resistors, capacitors, inductors, transmission
lines (and possibly other S/Y/Z models with symmetrical matrices) (i.e.
reciprocal) will create symmetrical S/Y/Z matrix, too. Structural
symmetry is not required. [A simplest example of non-reciprocal circuit
is controlled source (or active amplifier).]
Any reciprocal 2-port makes: S12 = S21, but generally not S11=S22.
With structural symmetry we get something more than just matrix
symmetry. Symmetrical 2-port (side A and side B identical) will also
give: S11 = S22.
Vladimir
-----Original Message-----
From: ibis-interconn-bounce@xxxxxxxxxxxxx
[mailto:ibis-interconn-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Thursday, January 14, 2010 10:16 AM
To: IBIS-Interconnect
Subject: [ibis-interconn] Touchstone Interconnect Causality, Passivity
and Symmetry
All,
Touchstone Interconnect Causality, Passivity and Symmetry
We all have agreed that interconnect is Causal and Passive.
Causal is a property of a Transfer Function (Framis), and basically says
a stimulus on one port must arrive at other ports at a later time.
Passivity is a property of the values of the Transfer Functions (Framis)
at a specific frequency, and basically says that more energy cannot come
out of ports than goes into ports.
There is no rule that says an interconnect Touchstone file is symmetric.
It is only symmetric if the interconnect is symmetric. A two port
package model often has a wire bond at one end, and a package pin at the
other end. In this case S12 != S21.
Walter
Walter Katz
303.449-2308
Mobile 720.333-1107
wkatz@xxxxxxxxxx
www.sisoft.com
--
Bob Ross
Teraspeed Consulting Group LLC Teraspeed Labs
121 North River Drive 13610 SW Harness Lane
Narragansett, RI 02882 Beaverton, OR 97008
401-284-1827 503-430-1065
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Teraspeed is a registered service mark of Teraspeed Consulting Group LLC
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