Re: Grounded via "fences" between microstrips




Joel Kolstad wrote:
I've been following some Hittite layout guidelines for a PCB layout; they
suggest using something of a hybrid co-planar waveguide (with ground)
/microstrip layout for the best isolation between two signal
traces(http://www.hittite.com/company_info/content_files/pdfs/appnotes/layout_guidelines_for_mmic_components.pdf).
However, I also happened to come across this paper -->
http://americas.kyocera.com/kai/semiparts/pdfs/pdfs/7292532_Aguirre_IMAPS_Denver2006_ViaIsolation_v2.pdf
that suggests that -- given practical via hole size constraints -- *no* vias
provide the best isolation.

You seem to be comparing apples and pears - the Hittite guidline is
talking about using a four layer stack to provide an environment where
you can layout sensible constant-impedance traces - it doesn't say
anything about using grounded track on the same layer as signal tracks
to improve isolaton, while the Kyocera paper is very specifically about
such grounded tracks, reinforced with grounded vias (a via fence).

Se if you can get hod of a copy of Howard W. Johson and Martin Graham's
"High-Speed Digital Design" ISBN 0-13-395724-1. Section 5.6 - pages
201-204 - talks about guard tracks.

--
Bill Sloman, Nijmegen

.