[SI-LIST] Re: Does power/ground pair edege radiation noise really matter in the EMI test?
- From: Jory McKinley <jory_mckinley@xxxxxxxxx>
- To: steve weir <weirsi@xxxxxxxxxx>
- Date: Fri, 24 Dec 2010 10:25:40 -0800 (PST)
Hello Steve/All,
These are very good references in general, I have a good understanding (in my
own mind) of the topic and have run field solvers that highlight the tricky and
potentially dangerous resonance issue. Briefly and basically what we have
found
(in several products):
(1) Every metal structure has the potential to resonate regardless of whether
its a plane, signal, or other.
(2) Ideally every metal structure in your system will be designed to have a
fundamental resonance below the highest critical frequency.
(3) Number (2) is a fantasy for most of us, so we rely on techniques (such as
stitching Vias, structure reduction) to move the critical resonances. This is
where the field solver comes into play. We attempt to capture the coupling
matrix from structure to structure.
(4) Resonances are unavoidable in practice, just because they exist does NOT
mean they will transfer. Natural isolation through Cap/Inductance,
dramatically
different source/load terminations and so on will determine how the cavity
energy or resonance will transfer or couple from structure to structure.
Merry Christmas all,
-Jory
________________________________
From: steve weir <weirsi@xxxxxxxxxx>
To: Jory McKinley <jory_mckinley@xxxxxxxxx>
Cc: Istvan Novak <istvan.novak@xxxxxxx>; liuluping 41830
<liuluping@xxxxxxxxxx>;
si-list@xxxxxxxxxxxxx
Sent: Fri, December 24, 2010 11:13:37 AM
Subject: [SI-LIST] Re: Does power/ground pair edege radiation noise really
matter in the EMI test?
Jory, this is a good application for a field solver. For some insight,
I would recommend both Cosmin Iorga's book and Madhavan Saminathan's
book. Fundamentally, without something that has real loss where you
want it, that energy is going to bounce around. Adding reflection
boundaries can move the X-Y locations of the peaks, and the peak
frequencies, but they don't dissipate. If you can, adjust the structure
so that it does not resonate strongly where you have a bunch of signal
energy to excite it.
Best Regards,
Steve
Jory McKinley wrote:
> Steve/Istvan/All,
>
> Might be interesting and along these lines, We are looking at a critical
> Power
>
> Plane which is feed from 20 locations above in a nice tight ring creating
> resonances at 2Ghz, 6Ghz, 10Ghz in the cavity. 10Ghz is critical, the good
> news is that the isolation from plane to source is excellent (below
> -60dB@10Ghz) at all 20 locations so I am not too concerned with this
> resonance
>
> coupling into each other. What is a concern and you mentioned it is other
> signal/power Vias that have no choice but go through this cavity. There is
> a
> natural filter in the inductance/cap of the Via which should isolate many of
> these signals from this resonance (the coupling from Plane to chip is under
> -50dB @10Ghz worst case). Additionally, It does appear that each signal (or
> pair) have one ground Via electrically nearby. There also is stitching of
> the ground above and below every 1/8 wavelength@10Ghz which should ensure
> containment.
>
>
> Any thing else......
>
>
> -Jory
>
> ________________________________
> From: Istvan Novak <istvan.novak@xxxxxxx>
> To: liuluping 41830 <liuluping@xxxxxxxxxx>
> Cc: si-list@xxxxxxxxxxxxx
> Sent: Thu, December 23, 2010 9:19:34 AM
> Subject: [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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