There is an excellent reference to using partitioning (gaps) in Mark
Montrose's book:
"Printed Circuit Board Design Techniques for EMC Compliance"

The audio & video sections in the Interconnects and I/O chapter
incourage the use of moating to seperate the analog and digital ground
plane sections.
I've used moating extensively in my circuit designs andthey work
quite well in supressing noise and crosstalk.
Mark Montrose supports the theory of  the "return path" in his book.

Another reference is Howard Johnson and Martin Graham's
"High Speed Digital Design A Handbook of Black Magic"
The following is taken direcly from Howard and Martins book:

At low speeds, current follows the path of least resistance. In
reference to
Figure 5.1, low speed current transmitted from A to B returns to the
driver
along the ground plane. The current density along each arc corresponds
to the conductance of that path.
At high speeds, the inductance of a given return current path is far
more
significant than it's resistance. High-speed return currents follow the
path
of least inductance, not the path of least resistance.
The lowest inductance return path lies directly under a signal
conductor.

These two books are the bible for me when working with high speed
transmission lines. I reccomend adding them to your shelf of reference
data.

Raymond Smith
Senior PWB Designer
TELLIUM
2 Crescent Place
Oceanport, N.J. 07757
732-923-4135
[log in to unmask]


Dave Schaefer wrote:

> I'm looking for information regarding SPLIT GROUND PLANES.
>
> Experts on grounding, EMI, EMC are teaching that gaps in ground planes
>
> create serious problems.  Component manufacturers, however, continue
> to
> recommend placing gaps under components (such as A/D's and D/A's).
>
> Can anyone:
>
> - point me in the direction of theoretical reference material
> - relate their experiences / practices
>
> Thanks,
> --
> Dave Schaefer
> Phone
> : (204)631-2298
> Senior PWB Designer                                         FAX :
> (204)631-2475
> NORTEL - Broadband Wireless Access          email : [log in to unmask]
> 37 Stevenson Road
> Winnipeg, MB R3H 0H9
>
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