[SI-LIST] Re: Guard Traces

  • From: Aaditya Kandibanda <aaditya.kandibanda@xxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Thu, 8 Mar 2012 19:19:48 -0800

Hello everyone,
Thanks you very much for your response I gained lot of information

-Aaditya

On Thu, Mar 8, 2012 at 10:52 AM, Lee Ritchey <leeritchey@xxxxxxxxxxxxx>wrote:

> With all the feedback on this forum that guard traces are a bad idea, why
> is this discussion still going on?  Are there still people who cling to the
> notion that guard traces are useful, even in the face of mounting evidence
> that they don't help?
>
>
> -----Original Message-----
> >From: Dennis <dennis.han@xxxxxxxxx>
> >Sent: Mar 7, 2012 12:59 PM
> >To: si-list@xxxxxxxxxxxxx
> >Subject: [SI-LIST] Re: Guard Traces
> >
> >In addition to what Wolfgang has stated, if the guard traces are too
> close to the signal traces, and most people who believe in ground traces
> put them too close (ground fill also falls in this category), the impedance
> of the signal traces is lowered and there are less crosstalk and radiation
> because of it if the now mismatched terminations don't cause other problems.
> >
> >
> >
> >
> >
> >--- In si-list@xxxxxxxxxxxxxxx, Gwen and Wolfgang <gwmaichen@...> wrote:
> >>
> >> Hello,
> >>
> >> first, the short answer: simply don't use guard traces here, they won't
> >> help much with isolation of high speed signals, and they use up way too
> >> much routing space (on all layers, because of the stitching vias
> >> necessary). Much easier to just increase the distance between diff pairs
> >> etc. and you get the same benefit. (in fact, I suspect the reason many
> >> people believe in the magic power of guard traces in this setting - high
> >> speed signaling - is because those traces _force_ you to have enough
> >> space between signal lines...). Guard traces have their place in
> >> low-current / low-leakage / high-voltage applications, but NOT in high
> >> speed digital. At least that's my opinion.
> >>
> >> If you do need grounded traces, stitch them to the ground planes with
> >> vias spaced no further than a quarter wavelength from the signal trace
> >> and at an interval of no less than a quarter wave length from each
> >> other. The wavelength given of course by bandwidth connected with the
> >> signal rise time, BW = 0.33 / Tr, or a bit more conservatively, the knee
> >> frequency f_knee = 0.5 / Tr. No special termination needed at the ends
> >> of those traces because they are already solidly grounded along their
> >> full length.
> >>
> >> Wolfgang
> >>
> >>
> >>
> >>
> >> On 3/7/2012 7:31 PM, Aaditya Kandibanda wrote:
> >> > Hello Everyone,
> >> > I have few questions about the guard traces.
> >> >
> >> > 1. How do I terminate the guard traces?
> >> > 2. While using the guard traces for differential pair, how shall I
> place
> >> > them between the differential pair?
> >> > 3. How should I place the vias for guard traces?
> >> > 4. What are disadvantages of Guard traces?
> >> >
> >> > Thanks and regards
> >> > Aaditya
> >> >
> >> >
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>
> I just used the energy it took to get mad and wrote some blues.  Count
> Basie
>
> Lee W. Ritchey
> Speeding Edge
> P.O. Box 2194
> Glen Ellen, CA
> 707-568-3983
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