piclist 2000\06\06\222730a >
Thread: Filter Capacitors
face BY : Dan Michaels email (remove spam text)

David VanHorn wrote:
>Sockets with caps in them are marginally better than nothing at all (see
>above), but it's even worse, because you've provided a path past the cap on
>the ground side as well.

I've read that the long tiny leads on the caps in this case
represent such a large inductance that this kind of socket is
quite useless at higher frequencies.

>It's hard to show this without pictures, but a cap with tracks or leads out
>to power and ground tracks, especially thick ones, is much less than
>Using fat power tracks can be bad.  Narrow tracks are higher impedance to
>high frequencies, but are the same DC resistance (close anyway).  I use a
>wide track from the chip to it's bypass cap(s) and a narrow track from
>there back to system power. This is because in the high frequency domain, I
>want the current to come from the bypass cap, not from the system buss.

Interesting observations here. But this makes it sound like going to
"ground planes" would be the worst thing imaginable. I've read in the books
that narrow buss traces might cause a problem regarding "return currents"
for the "signals" routed from one chip to the next. Narrow traces -->
larger inductive loops --> more EMI/noise transmission.

Can you comment on this ??? [also see next]

{Quote hidden}

This kinda sounds opposite to what you said in the previous paragraph.

Solution --> narrow Vcc, but wide gnd leads ????? Can you illuminate??

- Dan Michaels
Oricom Technologies


See also: www.piclist.com/techref/logic/dsps.htm?key=filter
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