[SI-LIST] AW: Re: Reduction of crosstalk by using stitching vias between traces

Yes, x-talk is a matter of distance, and yes, talking about distance without 
relation to the tracewidth isn't accurate. That's why I also stated a distance 
in factors of tracewidth (the tracewidth is always related to the reference 
plane distance). There are quite good rules of thumb: >5x tracewidth distance 
between differentialtraces "removes crosstak" This works fine for most 
applications.

I don't like using Microstrip for Datarates exceeding 6GBps, but in some cases 
it is absolutely ok (and even better than stripline). If you have very short 
traces, Microstrip is better because you don't need to worry about via stub 
effects and reflections. The longer the trace, the more preferable it is to 
route it as stripline. Crosstalk and EMI are other factors to prefer stripline.

BR
Gert


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-----Ursprüngliche Nachricht-----
Von: Pehr Andersson [mailto:andersson.pehr@xxxxxxxxx]
Gesendet: Donnerstag, 5. Januar 2012 19:48
An: Havermann, Gert
Cc: si-list@xxxxxxxxxxxxx; Rick Brooks (ricbrook)
Betreff: Re: [SI-LIST] Re: Reduction of crosstalk by using stitching vias 
between traces

If we have in between differential traces, a single trace and stitch that one 
with thru hole vias connecting reference planes, then it's a guard trace, how 
much reduction in crosstalk could we then expect?

Also how wide should this single "guard trace" be, if the drill hole diameter 
of my stitching vias are 10 mils, is it OK if the trace is >
12 mils wide? (The gap is 30 mils wide)

So basically if I understood correctly only means we have for reduction of 
crosstalk is to increase the spacing between the pairs and also how close are 
the traces to the reference planes also affects crosstalk, but closeness to 
reference plane isn't something that I could change, since then the 
differential impedance changes, and I have to use smaller traces, which could 
be problematic from manufacturing point of view? Thinner traces will be more 
susceptible to impedance variations.

Is it recommendable to use microstrip traces for high-speed signaling where 
data rate is > 10Gb/s?

Since stripline is what is usually seen for high-speed Ethernet (10GBase-KR)

Thanks and best regards! //Pelle



> 2012/1/5, Havermann, Gert <Gert.Havermann@xxxxxxxxxxx>:
> Pelle,
>
> the effect is minimal. I'd guess, that you will reduce the x-talk of
> the microstrip by 2%,  and the stripline by 1% (attention: I'm talking
> about total reduction. I'm not saying stitching brings you down to 1% 
> x-talk!!!).
>
> Just for reference, 4 mil of additional separation between the
> differential pairs gives you approx, 5-10dB lower crosstalk (5dB
> microstrip, 10dB stripline depending on the topology). Having a
> separation of >3x the tracewidth in stripline already gives you approx 30dB 
> isolation (2% x-talk).
>
> Distance is much more effective for isolation than stitching vias.
>
> BR
> Gert

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