[SI-LIST] Re: Guard Traces - Use 'Em, or Not?

  • From: "Moran, Brian P" <brian.p.moran@xxxxxxxxx>
  • To: "bertsimonovich@xxxxxxxxxx" <bertsimonovich@xxxxxxxxxx>, "ken@xxxxxxxxxxxxxxxx" <ken@xxxxxxxxxxxxxxxx>, "EMC-PSTC@xxxxxxxxxxxxxxxxx" <EMC-PSTC@xxxxxxxxxxxxxxxxx>, 'SI-LIST' <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 25 May 2012 03:56:14 +0000

My quick 2 cents,

The effectiveness of guard traces depends on whether you are talking
microstrip or stripline. My understanding, based on a conversation with
Mr. Bogatin just this past week, and I don't mean to speak for him, is
that guard traces are pretty useless on microstrip layers. The fringe
fields more or less leap frog the guard trace to the victim. You get
about the same result by just extending the spacing as you would have
to anyway to implement the guard trace, and you avoid issues with
termination and standing waves. However, guard traces on stripline
layers can be useful if implemented properly. That's about all I can say.
I've never used guard traces in any designs.  


Brian Moran
Signaling Development Group
Client Platforms
Intel Corporation

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of Lambert Simonovich
Sent: Thursday, May 24, 2012 5:15 PM
To: ken@xxxxxxxxxxxxxxxx; EMC-PSTC@xxxxxxxxxxxxxxxxx; 'SI-LIST'
Subject: [SI-LIST] Re: Guard Traces - Use 'Em, or Not?

Ken et al,

Good blog post. I have been doing a little research myself; hopefully to put
the subject to bed. I was putting the finishing touches on a white paper
when you posted your link.

Abstract:
To guard or not to guard? That is the question often asked by digital
hardware design engineers. As bit rates continue to climb, there is
increased debate on whether to use guard traces to control crosstalk in
high-speed digital signaling.  By doing so, it is believed the guard trace
will act as a shield between the aggressor and victim traces.  On the other
hand, the argument is that merely separating the victim trace to at least
three times the line width from the aggressor is good enough.  This paper
studies the application of guard traces and quantifies the results against
non guarded scenarios.

Conclusions:
This study has shown that adding a guard trace, at 3 times the line width,
terminated at both ends with 50 Ohms, does little to improve crosstalk on
the victim. In fact, in most cases, it was worse. The same was true when the
guard trace was grounded only at each end. But adding a ground-stitched
guard trace, with the same spacing, showed it was the best solution for
microstrip, and had little to no benefit for stripline. However, by
increasing the spacing to 5 times the line width in microstrip, the
crosstalk, for all intensive purposes, was the same. In stripline, there was
no benefit in adding a guard trace for digital signaling.

You can download a copy from my website. Hope everyone finds it useful. Here
is the link:

http://bit.ly/KSM5BZ

Best regards,

Bert Simonovich, Consultant & Founder
LAMSIM Enterprises Inc.
"Innovative Signal Integrity and Backplane Solutions"
Email: lsimonovich_at_lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/
LinkedIN: http://www.linkedin.com/in/bertsimonovich
Web Site: http://lamsimenterprises.com/

=======================================================

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Ken Wyatt
Sent: May-24-12 2:43 PM
To: EMC-PSTC@xxxxxxxxxxxxxxxxx; SI-LIST
Subject: [SI-LIST] Guard Traces - Use 'Em, or Not?

Hi Group,
After noticing the continued banter and discussions regarding guard traces
in both the EMC and SI groups over the past months, I decided to consult a
couple experts on the subject - Howard Johnson and Eric Bogatin. I
summarized their thoughts in my latest blog posting on the Test &
Measurement World web site:
http://www.tmworld.com/blog/The_EMC_Blog/41806-Guard_Traces_Use_Em_or_Not_.p
hp. I invited both to add any additional comment, if they wished. Feel free
to add to the discussion.

Cheers, Ken
_______________________
Kenneth Wyatt
Wyatt Technical Services LLC
Woodland Park, CO
Email Me! | Web Site | Blog
Subscribe to Newsletter
Connect with me on LinkedIn


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