[SI-LIST] Re: off-diagonal resistance and conductance elements
- From: Anshuli Goel <anshuli@xxxxxxxxxxxx>
- To: tony_dunbar@xxxxxxxxxxx
- Date: Wed, 19 Feb 2003 14:59:02 +0530
My understanding with L11 and C11 was that L11 does not include the effect of
neighboring nets while C11 does
i.e. L11 is self parasitics while C11 = C1g + C12
Any explanations ?
Anshuli
"Dunbar, Tony" wrote:
> 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?
>
> 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
>
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