Re: PCB Design

From: John Larkin (jjlarkin_at_highSNIPlandTHIStechPLEASEnology.com)
Date: 08/09/04 

Date: Mon, 09 Aug 2004 10:19:41 -0700

On Mon, 9 Aug 2004 16:54:10 +0200, "Anders F" <af-spam@hi5.dk> wrote:

>Hmm. I'll just sum the points *most* agree on:
>
>Planes are good. Close planes are better!

Exactly. The planes form a combination ultra-low impedance
transmission line and a microwave-quality, nicely lossy capacitor.

>Low inductance in the caps is imortant. Use small / wide caps, very short
>traces and multiple vias.

Not really. The planes are the real HF bypass, and the caps help out
at low frequencies.

>Numbers count. Multiple capacitors lowers the overall inductance.

No; see above. The capacitors add, well, capacitance. The inductance
that a part sees is dominated by its leads and the traces and vias to
the planes.

>Then the "details" like actual numbers and values, that's scary. Presently
>I'm primarily a bit puzzled about the effect of caps above their resonance
>frequency.

If you accept my theory, it all becomes very simple.

John

Relevant Pages

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  • Re: PCB Design
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