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

  • From: <Christopher.Jakubiec@xxxxxxxxxxxx>
  • To: <doh@xxxxxxxxxx>, <bertsimonovich@xxxxxxxxxx>, <ken@xxxxxxxxxxxxxxxx>, <EMC-PSTC@xxxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Fri, 25 May 2012 16:49:58 +0000

So, physics aside let's ask the question how many people have chosen to 
implement guard traces into their designs as an optimal solution?

Regards,

Chris
Infineon


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of Oh, Dan
Sent: Friday, May 25, 2012 9:35 AM
To: bertsimonovich@xxxxxxxxxx; ken@xxxxxxxxxxxxxxxx; 
EMC-PSTC@xxxxxxxxxxxxxxxxx; 'SI-LIST'
Subject: [SI-LIST] Re: Guard Traces - Use 'Em, or Not?

Hi Bert,

Thanks for great data and paper. We can finally discuss this issue over real 
data!
As I have mentioned in the earlier posting, the guard trace effectiveness 
strongly depends on the trace height and spacing. The capacitive (electrical) 
coupling saving by placing the guard trace is pretty minimal as others pointed 
out. However, I believe the main advantage of the guard trace is reducing the 
inductive (magnetic) coupling which decays rather slowly than the capacitive 
coupling.

The example you used only had 3mils height and 5mils spacing which makes the 
most of signal return through the ground plane rather than the guard trace. It 
is not surprising that you would not see much improvement in this case. If you 
increase the height, you will definitely see the improvement (say 15mils). Of 
course, this may not be a typical conventional microstrip configuration.

The point I am trying to make is that let's not make a myth out of this guard 
trace. It is a simple physics. If the trace ground plane further away, use the 
guard trace (of course with proper stitching and impedance matching). 
Otherwise, don't. It would be nice if you can re-simulation your case with 
various heights.

Best,
-Dan Oh
___________________________________________
Dan (KyungSuk) Oh, Ph.D.
Technical Director of Signal and Power Integrity
Rambus Inc.
(B) 408-462-8363


-----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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