[SI-LIST] Re: More About Plane Isolation
- From: Hirshtal Itzhak <ihirshtal@xxxxxxxxxx>
- To: shlepnev@xxxxxxxxxxxxx
- Date: Thu, 21 Jul 2011 08:07:22 +0200
Hello Yuriy,
Thanks to you and everyone who has responded.
Regarding the hole(s) coupling: Would it be safe to constrain the
distance of the traces from the hole(s) to a large enough distance such
that if there was a trace instead of the hole(s) the crosstalk on this
trace was smaller than permitted?
Best Regards
Itzhak Hirshtal
-----Original Message-----
From: Yuriy Shlepnev [mailto:shlepnev@xxxxxxxxxxxxx]
Sent: Friday, July 15, 2011 2:53 AM
To: Hirshtal Itzhak
Cc: si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] More About Plane Isolation
Itzhak,
The coupling through a small hole is extremely broadband and almost
frequency independent. Though, the value of the coupling is very small
to
worry about for digital signal integrity problems. However it is
considerably larger comparing to coupling through a solid metal plane.
It
may be important to put some restrictions on distance from strip to
holes
for digital to analog interference problems. That can be done with the
electromagnetic analysis.
Best regards,
Yuriy
Yuriy Shlepnev
www.simberian.com
-----Original Message-----
From: Hirshtal Itzhak [mailto:ihirshtal@xxxxxxxxxx]
Sent: Thursday, July 14, 2011 4:49 AM
To: shlepnev@xxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] More About Plane Isolation
Hello Yuriy,
Thanks again. As I understand the Bethe hole directional coupling you
mentioned (and I admit to be far from an expert on this issue), it seems
to
be of a narrow band nature. If I'm right, then it seems relatively
irrelevant to regular wide-band digital signals I'm concerned with,
isn't
it?
Best Regards
Itzhak Hirshtal
-----Original Message-----
From: Yuriy Shlepnev [mailto:shlepnev@xxxxxxxxxxxxx]
Sent: Wednesday, July 13, 2011 4:06 AM
To: Hirshtal Itzhak
Cc: si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] More About Plane Isolation
Itzhak,
In addition to Steve's response, I can add a few things.
A hole much smaller then the wavelength may serve as a coupling
structure.
Search for Bethe hole directional coupler or see the original H.A. Bethe
paper (Phys. Rev. vol. 66, 1944, Oct. p. 163-182) for more details. With
appropriate location of a hole and strips, the coupling may be much
larger
then coupling through the solid conductive planes even at lower
frequencies.
Coupling through a hole filled with a metal post (screw) may be larger
or
smaller - it depends on whether the screw is connected to the solid
conductive planes or not (and other elements of geometries of coupled
structures). If multiple holes appear along a strip line, the coupling
will
increase substantially comparing to the case with one hole or to the
solid
plane. Periodicity will increase the coupling, but only at frequencies
with
the distance between the holes equal to a quarter of wavelength. Only
electromagnetic analysis may provide guidelines for the isolation in
your
design.
Best regards,
Yuriy
Yuriy Shlepnev
www.simberian.com
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Hirshtal Itzhak
Sent: Tuesday, July 12, 2011 12:02 AM
To: shlepnev@xxxxxxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] More About Plane Isolation
Hello Yuriy,
It took me a while, because I've lost my SI-LIST correspondence, but
still,
I would like to question your note about through-plane coupling via PCB
holes, which I cite below (from the SI-LIST Archive).
First, is it true that the coupling through a single hole will be very
low
at frequencies that correspond to wavelengths longer than twice the hole
diameter?
Second, what if the hole isn't really a hole, since it's filled with
copper,
or "filled" with a screw? This will turn the hole to a much less
coupling
structure, isn't it?
Third, can you explain the issue of periodic hole pattern? Is it an
issue at
several GHz frequencies?
Thanks
Itzhak Hirshtal
Your Note:
Note, that these results are for the solid copper planes. If planes have
holes in vicinity of the traces, the coupling may substantially increase
at
high frequencies even for much shorter segments. If small holes form a
periodic pattern, the structure may behave as very effective directional
coupler with substantially larger coupling at microwave frequencies.
As Scott already pointed out, you have to do numerical analysis for a
structure that represents your particular design.
Best regards,
Yuriy
www.simberian.com
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addressee, please be aware
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