[SI-LIST] Re: Relativity in EMC design

["Mangipudi, Prasad" <Prasad_Mangipudi@xxxxxxxxxxx>]

Hi Zhangkun,

There are many ways to skin a cat.  A simple approach is to reduce the diel=
ectric thickness between the top layer and the next ground plane.  This wil=
l reduce the loop area and so radiation but also reduces the impedance of t=
he trace.  If you have a range of impedance that you can work with, then de=
liberately reducing the impedance as above will reduce the radiation. Other=
 things like good stackup (all signals referenced to ground) and good high =
speed design practices are always required.

Good Luck!
Prasad

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On=
 Behalf Of Zhangkun
Sent: Tuesday, May 13, 2008 3:04 AM
To: si-list
Subject: [SI-LIST] Relativity in EMC design

Hi all

Currently, we have measured the radiation of signal line on external layer =
of PCB. Based on the measurement result, we could gotten some design-guidel=
ine for layout.

For example, there is a  external line of 6000mil. When the stimulus is 5mV=
 at 400MHz, the RE radiation at 3m is 40dbuV/m. The FCC RE limitation is 47=
dbuV/m. There is remaining margin of 7db.

My question is 7db is enough or not. On the PCB, there will be more than on=
e line, which carry signal of 400MHz. The RE radiation maybe reinforce. How=
 to evaluate the relativity effect of diffrent line carrying 400MHz signal?

Any advice will be helpful.

Best Regards

Zhangkun
2008.5.13

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• References:
  • [SI-LIST] Relativity in EMC design
    • From: Zhangkun

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