[SI-LIST] Re: AW: Is the ground via helpful to reduce the EMI radiation?
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: wolfgang.maichen@xxxxxxxxxxxx
- Date: Tue, 13 Oct 2009 14:12:42 -0400
Wolfgang
With all due respect. The Sun paper discusses vias w.r.t. cavity
excitation and crosstalk. No where in the paper is EMI, emissions, or
radiation discussed.
Cavity mode excitation due to via penetration, and peaking of via
crosstalk due to quarter-wave stub resonances are well-known
phenomena. These may contribute to emissions, if, and only if, there
is a suitable radiating element exposed to the universe. In boards with
ground planes surrounding the cavities and vias, and no parasitic
coupling to other unshielded structures, such as cables and poorly
designed packages, radiation is minimal. It is the other structures
that radiate the energy that is peaked by resonances.
regards,
Scott
-
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
wolfgang.maichen@xxxxxxxxxxxx wrote:
>
> Here is a recent paper that deals with some aspects of this questions:
>
> Gustavo Blando, Jason Miller, Doug Winterberg, Istvan Novak
> "Cross Talk in Via Pin Fields, Including the Impact of Power
> Distribution Structures"
> DesignCon2009, Santa Clara, CA, February 2-5, 2009
>
> Wolfgang
>
>
>
>
>
>
> *Scott McMorrow <scott@xxxxxxxxxxxxx>*
> Sent by: si-list-bounce@xxxxxxxxxxxxx
>
> 10/13/2009 09:38 AM
>
>
> To
> Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
> cc
> Bob Wang <b0b.wan9@xxxxxxxxx>, Gert Havermann
> <Gert.Havermann@xxxxxxxxxxx>, si-list <si-list@xxxxxxxxxxxxx>
> Subject
> [SI-LIST] Re: AW: Is the ground via helpful to reduce the EMI radiation?
>
>
>
>
>
>
>
>
>
> I'm with Lee on this one. I fail to see how an "antenna" that is 95%
> buried under ground planes can radiate to a significant extent. Now
> package leads and planes that form patch antennas, I get.
>
> Lee Ritchey wrote:
> > Have you any proof that vias radiate or is this just speculation?
> Or for
> > that matter, that the discontinuity causes radiation?
> >
> >
> >
> >> [Original Message]
> >> From: Bob Wang <b0b.wan9@xxxxxxxxx>
> >> To: Havermann, Gert <Gert.Havermann@xxxxxxxxxxx>; si-list
> >>
> > <si-list@xxxxxxxxxxxxx>
> >
> >> Date: 10/13/2009 9:02:39 AM
> >> Subject: [SI-LIST] Re: AW: Is the ground via helpful to reduce the EMI
> >>
> > radiation?
> >
> >> Thanks, Gert!
> >> I'm handling 6.75Gbps differential signals in my design. I agree
> with you
> >>
> > that the discontinuity creates x-talk and radiation, some energy is
> > transferred from differential mode to common mode, then the energy is
> > radiated from the via stub like a dipole antenna.
> >
> >> Bob Wang
> >>
> >> ----- Original Message -----
> >> From: <Gert.Havermann@xxxxxxxxxxx>
> >> To: Bob Wang; si-list
> >> Cc:
> >> Date: 2009-10-13 Time: 15:30:11
> >> Subject: AW: [SI-LIST] Is the ground via helpful to reduce the EMI
> >>
> > radiation?
> >
> >>> Hi Bob,
> >>>
> >>> I don't know of any direct relationship between stublength and
> >>>
> > radiation. Based on my experience, increasing via stublength increases
> > reflections on the transmission line. Of course these reflections
> can cause
> > standing waves and thus radiation, but not necessarily.
> >
> >>> Usually the traces and planes are the root for radiation. they can act
> >>>
> > as monopole or loop antenna. The via stub would start to radiate when
> > exceeding 1/7 of the wavelength. For example this is 270 mil at 3GHz
> > (approx 6GBps). Thats a really thick PCB.
> >
> >>> So much about radiation, now back to your question if GND vias
> adjacent
> >>>
> > to the via help to improve EMI. Yes, they do. This is due to the
> improved
> > GND return path. Without GND vias close to the signal via, you
> generate a
> > huge GND-return discontinuity because the GND-currents can not
> follow the
> > signal as close as they want.
> >
> >>> This kind of discontiuity creates x-talk and radiation, making the
> >>>
> > design less tolerant to EM-disturbance.
> >
> >>> I hope this helps.
> >>>
> >>> BR
> >>> Gert
> >>>
> >>>
> >>>
> >>>
> >>>
> >>
> --------------------------------------------------------------------------
> >>
> >>> Absender ist HARTING Electronics GmbH & Co. KG; Sitz der Gesellschaft:
> >>>
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> > pers?nlich haftende Gesellschafterin: HARTING Electronics Management
> GmbH;
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> >
> >>> -----Urspr¨¹ngliche Nachricht-----
> >>>
> >>> Von: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >>>
> > Im Auftrag von Bob Wang
> >
> >>> Gesendet: Dienstag, 13. Oktober 2009 06:58
> >>> An: si-list
> >>> Betreff: [SI-LIST] Is the ground via helpful to reduce the EMI
> radiation?
> >>>
> >>> Hi All,
> >>>
> >>> As far as I know, long via stub will bring more radiation than
> short via
> >>>
> > stub and make the EMI to be worse.
> >
> >>> I'm wondering if I put a ground via closed to the long via stub will
> >>>
> > reduce the radiation and improve the EMI performance?
> >
> >>> Any suggestions are appreciated.
> >>>
> >>> Bob Wang
> >>> 2009-10-13
> >>>
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> --
> Scott McMorrow
> Teraspeed Consulting Group LLC
> 121 North River Drive
> Narragansett, RI 02882
> (401) 284-1827 Business
> (401) 284-1840 Fax
>
> http://www.teraspeed.com
>
> Teraspeed® is the registered service mark of
> Teraspeed Consulting Group LLC
>
>
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--
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
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