Re: [SI-LIST] : Guard traces

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From: Tadashi ARAI (arap@jdc.paso.fujitsu.co.jp)
Date: Wed Jun 21 2000 - 17:18:28 PDT


Howdy All,

I have attached 2 waveforms what show crosstalk noise with/without guard
traces, our staff's (old) analysis by XTK.

Configurations are;

 Surface of 4 layer board (microstrip),
 Dielectric (FR4) height : 4.33mils
 Copper Foil : 0.709mils

5 traces;
 Width : 5mils
 Space(edge-edge) : 20mils
 Length : 8inchs
Center one is inactive, measured trace (victim).
Another 4 are given stimulus simultaneously (aggressor).
These show FEXT results only.

5mil_L_d.gif:
 inserting guard traces of 5mils width between each traces.
 Red: No guard traces (only AIR gap)
 Blue: with guard traces modeled as transmission line with via of 1"
 each
 Black: with guard traces modeled as ideal ground

18mil_L_d.gif:
 inserting guard traces of 18mils width ("Flood") between each traces.
 Red: No guard traces (only AIR gap)
 Blue: with guard traces modeled as transmission line with via of 1"
 each
 Black: with guard traces modeled as ideal ground

However I know these analysis are not properly modeled and we have much
to do, I guess we have got some ideas what couplings tend to.

At least, we can avoid to make layout designer change our target
geometry arbitrary with guard traces :).

And some one please tell me the inadequacy of guard traces at the range
of our design - around 1GHz.

Regards,
//// /// // / / / / / / / / / /
Tadashi Arai//Platform Developing Dept.,Desktop Prd Div. Fujitsu Limited
arap@paso.fujitsu.co.jp TEL:+81-42-370-7624 Inagi-shi, Tokyo, Japan
/ / / / / / / / / / / // ///
On Tue, 20 Jun 2000 08:15:59 -0800
Mail from cadpro2k@dacafe.com described as below:

> Hi Tadashi,
>
> Did you run a simulation with only an airgap between the traces (same
> distance you have with the guard traces on the board) to show you what
> your crosstalk would be with only the added separations? Try that, and
> report back what you find. (Pssst, guard traces aren't necessary) :)
>
> -M-
>
>



5mil_L_d.gif

18mil_L_d.gif

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