[SI-LIST] Re: guard traces (huge)
- From: "Istvan NOVAK" <istvan.novak@xxxxxxxxxxxxxxxx>
- To: <moshef@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Sun, 18 Jul 2004 11:06:11 -0400
Moshe,
As this topic came up in the past on this list, you can also
search the archives for previous comments.
My brief summary is this: guard traces work like lightning rods,
by attracting stray field that otherwise would end up on victim
lines, creating crosstalk. A guard trace with width similar to
that of regular traces will give an additional 6-15 dB isolation
(base line: crosstalk between two lines with a fixed spacing,
guard trace not present). Note that in microstrip far field,
crosstalk drops quadratically with spacing. In stripline, crosstalk
drops with the fourth power of spacing, so it is always prudent to
spread traces first as much as room permits. In wide digital buses,
guard traces between all adjacent trace combinations is not very
practical, mostly because you also need a sufficient number of vias
stitching the guard traces to ground to break up the resonators
created by the grounded-ended guard traces. The minimum stitching
distance should be less than the wavelength at the bandwidth of signals.
Guard traces may be effective protecting a few sensitive lines,
mostly in mixed analog-digital systems. Buffered guared traces
can also reduce the impact of surface conduction and stray
capacitance in instrumentation amplifiers.
Best regards,
Istvan Novak
SUN Microsystems
----- Original Message -----
From: "Moshe Frid" <moshef@xxxxxxxxxxx>
To: <si-list@xxxxxxxxxxxxx>
Sent: Sunday, July 18, 2004 11:26 AM
Subject: [SI-LIST] guard traces (huge)
> Hi All
> can someone tell me something about rules of guard trace
> what space need to be kept
> do they have to be connected to the ground plane and how do they affect
> the impedance of the trace that is guarded ?
>
>
> Moshe Frid
> Adcom pcb design
>
> Mobile :066-573232
>
> Tel. 972-9-7417411 (108)
>
> Email:moshef@xxxxxxxxxxx
>
>
>
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