[SI-LIST] Re: off-diagonal resistance and conductance elements
- From: "Issa, Elie" <Elie.Issa@xxxxxx>
- To: <tony_dunbar@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 19 Feb 2003 14:11:53 -0600
Tony:
My understanding also is that L11 is the self inductance. So I ran
the XFX field solver to validate my thoughts, a single conductor and =
dual conductor microstrip with=20
10mils spacing microstrip and compare L11. Here are the reports
Configuration Name: X2 Conductors: 2
Conductor index: 0 name: $$GND$$=20
Conductor index: 1 name: A=20
Conductor index: 2 name: B=20
i j Lij Cij Ze Zo Se So Fwdx =
Rvsx =20
from to (nh/in) (pf/in) (ohms) (ohms) (ns/ft)(ns/ft) (s/s) =
(v/v)=20
-------------------------------------------------------------------------=
-
1 1 8.882 2.510 59.91 - 1.78 - - -
1 2 1.568 0.199 67.24 51.96 1.86 1.69 0.099 =
0.128
2 2 8.877 2.510 59.89 - 1.78 - - -
;
Configuration Name: X1 Conductors: 1
Conductor index: 0 name: $$GND$$=20
Conductor index: 1 name: A=20
i j Lij Cij Ze Zo Se So Fwdx =
Rvsx =20
from to (nh/in) (pf/in) (ohms) (ohms) (ns/ft)(ns/ft) (s/s) =
(v/v)=20
-------------------------------------------------------------------------=
-
1 1 8.905 2.505 59.63 - 1.79 - - -
;
If I reduce the spacing to 5mils, here are the results..
Configuration Name: XX Conductors: 2
Conductor index: 0 name: $$GND$$=20
Conductor index: 1 name: A=20
Conductor index: 2 name: B=20
i j Lij Cij Ze Zo Se So Fwdx =
Rvsx =20
from to (nh/in) (pf/in) (ohms) (ohms) (ns/ft)(ns/ft) (s/s) =
(v/v)=20
-------------------------------------------------------------------------=
-
1 1 8.756 2.596 59.57 - 1.76 - - -
1 2 2.534 0.445 72.44 45.23 1.87 1.65 0.125 =
0.231
2 2 8.756 2.596 59.57 - 1.76 - - -
;
Configuration Name: X Conductors: 1
Conductor index: 0 name: $$GND$$=20
Conductor index: 1 name: A=20
i j Lij Cij Ze Zo Se So Fwdx =
Rvsx =20
from to (nh/in) (pf/in) (ohms) (ohms) (ns/ft)(ns/ft) (s/s) =
(v/v)=20
-------------------------------------------------------------------------=
-
1 1 8.905 2.505 59.63 - 1.79 - - -
;=20
In both cases, there seem to be only small difference between the self =
inductance=20
of single line and L11 in the coupled line matrice. =20
Regards
Elie
-----Original Message-----
From: Dunbar, Tony [mailto:tony_dunbar@xxxxxxxxxxx]
Sent: Tuesday, February 18, 2003 4:41 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: off-diagonal resistance and conductance elements
For the purposes of clarification:-
Patrick initially stated "The on-diagonal parameters (e.g., L11) are
typically stated to be the self parasitics, ..."
My understanding is that, rather than being purely "self parasitics", =
they
actually include the effects of coupled neighbors. As a consequence, for
example, L11 will actually be different (lower) than it will be if the =
same
primary structure existed without any coupled neighbors.
Is that correct?
Thanks,
Tony Dunbar
-----Original Message-----
From: Zabinski, Patrick J. [mailto:zabinski.patrick@xxxxxxxx]
Sent: Tuesday, February 18, 2003 2:42 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? =20
For example, what does R12 respresent? With the lossless/ideal
case setting R12=3D0, 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,=20
in even-mode propagation, the return current is within the=20
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=20
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
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