Re: Expansion board decoupling specs

[Dimiter Popoff <tgi@bulnet.bg>]

Craig,
My advice to ignore the (de)coupling capacitors was wrong.

Richard, Chris,
I am also quite an analog guru and I am paranoid about decoupling.
But I was wrong for another, very simple reason, which I thought of
while I was taking my walk today: if the bus connectors are not
decoupled on the motherboard, then if one plugs just two cards
at a sufficienntly long distance from each other and one of these
cards does not AC-short all planes, the power lines will
not shield the signal lines between them and the system will not
work.

Of course, the better solution is to have all planes decoupled next
to the connectors at the motherboard - the bus will have more consistent
behaviour and signals running a long distance crossing empty slots
will be better guarded. A conservatiive designer would decouple
both places.


Dimiter

Dimiter Popoff
Transgalactic Instruments, Gourko Str. 25 b, 1000 Sofia, Bulgaria
http://www.freeyellow.com/members2/transgalactic/
Email: tgi@bulnet.bg, tgi_earth@yahoo.com
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