[SI-LIST] Re: Resistance Matrix & cross talk
- From: Raj Raghuram <raj.raghuram@xxxxxxxxxxxxxxx>
- To: joepaulm@xxxxxxxxx
- Date: Fri, 17 Mar 2006 07:58:33 -0800
To expand on what you quoted, there are two reasons for non-zero values
of off-diagonal values of the resistance matrix
1. If you an overlap in the return path, that could contribute to
off-diagonal terms. It is easier to visualize this in something like a
ribbon cable or connector where ground is also a conductor. Or a coaxial
cable with two inner conductors. For a coupled microstrip sufficently
separated, the return currents do not overlap at high frequencies and
the off-diagonal terms would tend to zero. At very low frequencies, the
values would be significant as the return currents spreads over the
width of the ground plane.
2. A second subtler reason for off-diagonal terms of the R-matrix is
that the current distribution in one conductor influences the current
distribution in the other. This effect is, again, more prominent at
higher frequencies. At very high frequencies, currents flow in a thin
layer near the surface and the nature of the distribution has a
significant effect on the loss.
On Thu, 2006-03-16 at 23:34, Joe Paul M wrote:
> Hi all,
>
> Can somebody give an explanion for R12 & R21 a near zero value in resistance
> matrix in crosstalk modelling.
>
> As per "Resistance Matrix in Crosstalk Modeling for Multiconductor Systems "
> by mentor graphics ,
>
> In general, a resistance matrix can be expressed as
> __ _
> [R] = | R11 R12 |
> | R21 R22 |
> -- ---
> where R11 and R22 are the sums of the resistance of the corresponding signal
> line and the resistance of a return path for each line at low frequency. The
> real part of the mutual impedance, R12, is related to the return path. If we
> consider an ideal return path (perfect conductor or very large return area),
> R12 will be close to zero and the resistance matrix will become diagonal at
> low frequency. However, in reality, the return path is not perfect ground
> and has some resistance. An ideal return path is a good assumption for
> low-frequency regime because the return current flow spreads throughout the
> entire return path or the ground plane to reduce the resistance.
>
> Does soembody have a lil more explantion for this?
>
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--
Raj Raghuram
Berkeley Design Automation (http://www.berkeley-da.com)
2902 Stender Way
Santa Clara, CA-95054-3213
Tel: 408.496.6600 x203
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email: raj.raghuram@xxxxxxxxxxxxxxx
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