[SI-LIST] Re: Question about pcb grounding
- From: "Grasso, Charles" <Charles.Grasso@xxxxxxxxxxxx>
- To: <leeritchey@xxxxxxxxxxxxx>, "Joel Brown" <joel@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 6 Nov 2007 09:41:45 -0700
On this one I agree with Lee completely.
Grounding must be designed based on the
product requirements.
Best Regards
Charles Grasso
Compliance Engineer
Echostar Communications Corp.
Tel: 303-706-5467
Fax: 303-799-6222
Cell: 303-204-2974
Pager/Short Message: 3032042974@xxxxxxxxx
Email: charles.grasso@xxxxxxxxxxxx
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Lee Ritchey
Sent: Tuesday, November 06, 2007 9:11 AM
To: Joel Brown; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question about pcb grounding
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?
>
> =20
>
> Thanks - Joel
>
> =20
>
>
>
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