[SI-LIST] AW: Is the ground via helpful to reduce the EMI radiation?
- From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
- To: "Bob Wang" <b0b.wan9@xxxxxxxxx>, si-list <si-list@xxxxxxxxxxxxx>
- Date: Tue, 13 Oct 2009 09:30:11 +0200
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
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-----Ursprüngliche 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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