[SI-LIST] Re: Guard traces for differential pairs

Hi Duane,

So how does one determine if it is magnetic or
capacitive crosstalk that is dominating in a
particular configuration?

Let's say I get two matrices from a field solver that
look like this:

C11 C12
C21 C22

and

L11 L12
L21 L22

Do I just look at how C12/C11 compares to L12/L11 and
how C21/C22 compares to L21/L22 ?

Thanks
Damon

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> 
> It also depends on the type of crosstalk: electric
> or magnetic (
> capacitive or inductive ).  If it's magnetic, guard
> traces won't help.
> If it's capacitive, guards will help but will leave
> you with the
> 'magnetic remainder' of the xtalk.
> 
> I've seen high impedance lines, more than 60 ohms,
> exhibit inductive
> xtalk.  My guess is guard traces would not have
> helped in this case.
> 
> Regards,
> Duane
> 
> > Sogo,
> > 
> > It is true that guard traces can INCREASE
> crosstalk, but
> > this can be avoided (and crosstalk in fact can be
> REDUCED)
> > if the via stitching is frequent enough.  Between
> each
> > stitching, there is a half-wavelength resonator,
> with a
> > lowest resonance frequency of fres=1/(2*tpd),
> where
> > tpd is the propagation delay between two stitching
> vias.
> > As long as the bandwidth of the signal on the
> structure
> > is safely below this resonance frequency, there
> should be no
> > problem with signal integrity.
> > 
> > Regards,
> > 
> > Istvan Novak
> > SUN Microsystems


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