[SI-LIST] Re: off-diagonal resistance and conductance elements
- From: "Raj Raghuram" <raghu@xxxxxxxxxxx>
- To: <zabinski.patrick@xxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 18 Feb 2003 18:04:12 -0800
Patrick,
Here are couple of scenarios where you can get an off-diagonal term for the
R matrix for a transmission line:
1. If the two conductors share a common return path, there could be a
voltage drop across the second conductor with respect to ground when current
flows in the first conductor. This could happen, for example, if a coupled
line is formed by two inner conductors in a coax. Another situation is a
microstrip or stripline where the conductors are close enough that their
ground currents overlap.
2. A second effect (though less important) is that the current distribution
across the area of cross-section of one conductor is influenced by current
in the other conductor. This again can be modeled by an off-diagonal term of
the resistance matrix.
Regarding off-diagonal conductance elements, the origin is similar to
off-diagonal terms of the C matrix. The G matrix can be viewed as the
solution obtained when the relative dielectric constant is made complex to
take care of loss tangent. G12 is due to current lines flowing from one
conductor to another just as C12 is due to electric field lines from one
conductor to another.
Best Regards,
Raj Raghuram
Sigrity, Inc.
"Achieve what others can't"
raghu@xxxxxxxxxxx
http://www.sigrity.com
4675 Stevens Creek Blvd. , Ste 130
Santa Clara, CA-95051
PH: 408-260-9344 x116
CELL: 408-390-7614
FAX: 408-260-9342
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Zabinski, Patrick J.
Sent: Tuesday, February 18, 2003 12:42 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] off-diagonal resistance and conductance elements
In a coupled-pair of distributed transmission lines (whether intentionally
for differential or unintentionally with crosstalk), most (good)
EM simulators produce a 2x2 matrix of capacitance, inductance,
resistance, and conductance (C, L, R, & G). The on-diagonal
parameters (e.g., L11) are typically stated to be the self
parasitics, which is quite easy to understand.
For the inductance and capacitance matrices, even the off-diagonal
parastics (e.g., L12, C21, ...) are easy to understand and
well published.
However, I have not been able to find a good description nor
treatment on the off-diagonal resistance and conductance
elements. Can anyone enlighten me a bit?
For example, what does R12 respresent? With the lossless/ideal
case setting R12=0, it cannot represent a resistive element
directly between the two traces. So what is it?
A second yet possibly related question deals with how these
matrices deal with odd- and even-mode using the same matrices.
When looking at any of the common twin-axial cables used
today with Infiniband and other differential protocols, the
two signal conductors are made with "good" (meaning low
loss) materials. In contrast, the outer shield is often
a much lousier (higher loss) material (either through the metallurgy
or thickness).
For odd-mode signals propagating down one of these twin-ax
cables, we believe the return current for one wire is
effectively captured (at least in part) in the other complement
wire, which would result in reasonably low loss. In contrast,
in even-mode propagation, the return current is within the
outer shield, which in turn results in a higher loss than
the odd-mode propagation. The end result (we have plenty
of measurement data confirming this) is that odd-mode
signals propagate reasonably well, but even-mode signals
attenuate and disperse much more significantly. (note:
for many applications, this is a very good thing.)
The question is: how can the LRCG matrices be set up such that you
use one set of matrices (in the form of a W-element if you wish) that
can accurately represent both cases? Does the off-diagonal
R & G matrices play a role?
Thanks,
Pat
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
