Re: [SI-LIST] : How to construct guard bands in Ansoft 2D

Eric Bogatin (bogatin@ansoft.com)
Fri, 29 May 1998 11:47:31 -0500

Since Charles Grasso sent a query to the SI reflector, and there may be others facing a similar question, I'd like to briefly describe exactly what he is trying doing and how to set this problem up in Ansoft's Maxwell 2D Extractor. For those of you who do not use Maxwell 2D Extractor, please ignore the following. For those of you who would like more information, please contact me off line.

After discussion off line with Charles, I understand his problem is to analyze the effect on the cross talk and characteristic impedance of signal traces which have ground traces adjacent to them, in addition to the top and bottom planes, as return paths. This design is often used for creating a virtual coax shield around the signal lines.

In the problem set up, each of the traces, signal and ground traces are drawn, in addition to the planes. In Maxwell 2D Extractor, only one conductor can carry the return path (ie, be labeled ideal ground), so all the conductors that are to be grounded; the "guard traces" and the planes, are grouped under the same name- labeled "ret_path", for example.

This group is assigned to be an ideal ground conductor. Maxwell 2D Extractor will automatically figure out the correct current distribution between all the conductors assigned to the ideal ground. When the solution is solved, the resulting matrix for the characteristic impedance, etc, is for the adjacent traces being part of the ground return network. The cross talk coefficients calculated are typically very, very small in this configuration.

--eric bogatin

At 10:21 AM 5/26/98 -0600, Grasso, Charles (Chaz) wrote:

>Does anyone know how to construct a guard band

>in Ansofts 2D extractor?

>

>Do I simply make the additional trace a non-ideal ground?

>

>Also I cannot seem to connect the trace to the ground

>to simulate a via?

>

>

>Thank you

>Charles Grasso

>EMC Engineer

>StorageTek

>2270 Sth 88th Street

>Louisville CO 80027 MS 4262

>grassc@louisville.stortek.com

>Tel:(303)673-2908

>Fax(303)661-7115

>Symposium Website URL: http://www.ball.com/aerospace/ieee_emc.html

>

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**********************************************************************

Eric Bogatin

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Ansoft Corporation

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