RE: [SI-LIST] : Guard traces

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From: George_Tang@Dell.com
Date: Wed Jun 21 2000 - 20:23:10 PDT


Tadashi,

From signal integrity perspective, your guard traces are fine. From EMI
perspective, at 1 GHz, you might have problems. The guard traces provide
greater mutual inductance between the signal trace and ground. But you will
not have perfect coupling (between signal and ground) until the signal
traces are placed between copper planes (stripline).

Regards,

George Tang

-----Original Message-----
From: Tadashi ARAI [mailto:arap@jdc.paso.fujitsu.co.jp]
Sent: Wednesday, June 21, 2000 5:18 PM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : Guard traces

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-
>
>

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