[SI-LIST] Re: 答复: Re: Does power/ground pair edege radiation noise really matter in the EMI test?

It is difficult to avoid the edge radiation, but you can try to diminish it
with some concept.
If you make the energy couple to ground from signals or powers more and
more, the radiation may be controlled.
Most PCBs are linear time-invariant system.
Linearity means either smaller source energy or slighter radiative PCB
channel, smaller radiated energy (y(t)=x(t)*h(t))
For example, try to thin the PCB layer to make the signals couple to
reference plane, or keep the key signals away from edge or sensitive area,
etc.
-best regards
-Long


2010/12/24 Xu Shuai <xushuai@xxxxxxxxxxxxxxxxxx>

> Hi Istvan
> Usually there are many clock signals and harmonics in a complex PCB, and
> there are also many high frequency resonances. So it is difficult to avoid
> the situation you mentioned in 3).
> But we can control the path of the critical net to avoid exciting the
> resonance, such as reference plane change, crossing split plane,etc. The
> Faraday cage is also a good solution.
> Best regards,
> Shuai
> -----ÓʼþÔ­¼þ-----
> ·¢¼þÈË: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> ´ú±í Istvan Novak
> ·¢ËÍʱ¼ä: 2010Äê12ÔÂ23ÈÕ 22:20
> ÊÕ¼þÈË: liuluping 41830
> ³­ËÍ: si-list@xxxxxxxxxxxxx
> Ö÷Ìâ: [SI-LIST] Re: Does power/ground pair edege radiation noise really
> matter in the EMI test?
>
> There are a large number of factors involved in such cases, making it
> practically not feasible to make generic rules based on test results on
> specific setups.  There are a few generic considerations though that
> may help.
> 1) Having a noisy power plane shape on the outside of the
> board stack-up will have a tendency to radiate like a patch
> antenna.
> 2) For internal power layers we can stitch the outside ground
> planes along the edge of the board, creating a Faraday cage, and
> pull back the planes to within the cage.
> 3) As always, resonances do not matter if we do not excite them,
> so you need to look at the resonance frequencies and the signals,
> which have a potential to excite those resonances to see if it in fact
> happens.
>
> Regards,
>
> Istvan Novak
> Oracle
>
> On 12/23/2010 5:53 AM, liuluping 41830 wrote:
> > Dear all:
> >
> >       The PDN noise voltages at the edges of a PCB are potential
> electromagnetic interference sources,the noise may be produced by SSN or
> cavity resonance. Many paper ,such as EBG technology,based on this
> suppose,but does this noise really matter in a typical digital board which
> include many high speed memory and serdes ?Does any test analysis that the
> plane edge noise account for how many percent in the  total radiation noise
> ?
> >
> >       Thanks and regards,
> >
> >         LIU Luping
> >
>
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