Pat

Ground traces around clock lines are only effective on outside layers.
On inside layers just leave the extra space around the clock trace, and
route between ground planes.
Spacing the traces more than 3 times the trace width apart doesn't reduce
crosstalk by much more.

An interesting book on this subject is "High Speed Digital Design - A
Handbook of Black Magic" by Johnson and Graham.

I do hope this is of some help on a subject were there are many different
opinions.

Joe Hurst
Computing Devices Canada




Pat wrote:

...
Next question is concerning special considerations for clock signals and
EMI.  Some of the Engineers want a ground trace surrounding the clock lines
and others say it would be better to just leave the space around the clock
line that the guard band would normally take up. The clock speeds are 40
Mhz and below using 6/6 on the inners and 8/8 on the outers. One of the 2
clock routing layers is next to the ground plane and the other layer is
next to the power plane.

All info is greatly appreciated!

Pat Paulson
VTEL Corporation
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