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

  • From: Ken Wyatt <ken@xxxxxxxxxxxxxxxx>
  • To: "Eric F. Steimle" <eric.steimle@xxxxxxxxxx>
  • Date: Fri, 25 May 2012 13:05:19 -0600

Eric, you missed April Fool's Day by a mile!  :-)
_______________________
Kenneth Wyatt
Wyatt Technical Services LLC
Woodland Park, CO
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On May 25, 2012, at 1:00 PM, Eric F. Steimle wrote:

> Personally I take it a step further and use guard traces for my guard traces. 
>   I find that gives me more guard traces.   On really critical boards I might 
> make a daughter card of guard traces and strap that to my main board.    My 
> next board is incredibly high performance so I'm thinking of making it out of 
> only guard traces, removing all traces and components to make room for more 
> of them.   I expect it to perform admirably ;)
> 
> -Eric
> 
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
> Behalf Of Christopher.Jakubiec@xxxxxxxxxxxx
> Sent: Friday, May 25, 2012 12:50 PM
> To: doh@xxxxxxxxxx; bertsimonovich@xxxxxxxxxx; ken@xxxxxxxxxxxxxxxx; 
> EMC-PSTC@xxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Guard Traces - Use 'Em, or Not?
> 
> 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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