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Thread: Filter Capacitors
www.piclist.com/techref/logic/dsps.htm?key=filter
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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
>optimum.
......
>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??

Cheers,
- Dan Michaels
Oricom Technologies
===================

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