[SI-LIST] Re: Question about pcb grounding
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Joel Brown" <joel@xxxxxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Tue, 6 Nov 2007 08:11:09 -0800
Joel,
That is just a very bad rule. Donb't know where it came from. Probably an
RE.
> [Original Message]
> From: Joel Brown <joel@xxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Date: 11/5/2007 4:01:42 PM
> Subject: [SI-LIST] Question about pcb grounding
>
> I have been reading some material regarding multipoint grounding of a pcb
to
> chassis ground.
> The recommendation is to have no more than 1/20 of a wavelength between
> grounding points.
>
> So at 500 MHz this is about 1 inch which clearly is not feasible in most
> applications.
>
> I'm guessing the reason for 1/20 wavelength is so that common mode noise
> generated on the pcb ground plane has a low impedance return path through
> the chassis structure from one section of the board to another. If the
> distance is much greater than that then there could be a high impedance
> (resonance) in the chassis return path and the common mode noise will go
> elsewhere. Am I right in my thinking here? What benefit is there to using
> multipoint chassis grounding when the spacing between ground points is
much
> greater than 1/20 wavelength which is what represents most design today?
>
>
>
> Thanks - Joel
>
>
>
>
>
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