Hi Ladies/Gentlemen,
I have been reading with interest the discussion articles on this
subject. Since Mike Violette 04/15/96 presented his opinion on VCC/GND
plane layout in multilayer board, the discussion seems to be focused
on PCB EMC design. Max Kelson 04/16/96 wrote:
[snip]
What this ferrite/cap configuration would do is to force the
oscillator to draw all transient current from the capacitor. Or, in
otherwords, the rest of the caps on the board would be unable to help
provide fast-transient current because of the ferrite. This would
keep the current loop (power AND GROUND) small and prevent it from
infecting the rest of the board. The path for the transient current
surges would be from the capacitor to the IC's power pin, out the
IC's ground pin and back to the negative side of the capacitor (a
relatively small loop).
[snip]
It might be worthwhile to pay attention to research work done by
professors at the Univ. of Missouri-Rolla. In the article "Power Bus
Decoupling on Multilayer Printed Circuit Board", IEEE Trans. on EMC,
vol. 37, pp. 155-166, May 995, they wrote:
[snip]
VI. Conclusion.
Unlike boards without internal power and ground planes, multilayer
boards have a built-in capacitance that is a more effective source of
current than surface decoupling capacitors at high frequencies. In the
time-domain, this means that most of the initial current supplied to a
fast switching device is provided by the interplane capacitance.
[snip]
Regards,
Barry Ma
