[SI-LIST] Re: Does power/ground pair edege radiation noise really matter in the EMI test?
- From: Jory McKinley <jory_mckinley@xxxxxxxxx>
- To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>, steve weir <weirsi@xxxxxxxxxx>
- Date: Mon, 27 Dec 2010 14:10:15 -0800 (PST)
Hello Lee,
We have a case in which an existing customer design was not functioning due to
one direct path to path coupling in the PLL. This path to path coupling was
one
resonate structure path (resonate at critical PLL frequency) to the PLL power
path. We came in and found the amount of coupling was in the -20dB range which
based on PLL simulations should have been less than -50dB at this critical
frequency. We caught this path on the old package (plus some others not
related
in separate blocks ) and spun a new package with coupling below the -50dB
target. The re-spun package is fully functional to date and trying to get
customer permission to turn into a paper.
There are other cases and admittedly more the common as you point out in which
it is less clear as to what the exact coupling path that has created issues
with
a product. For example, we are working on which shows at least 5 coupling
paths
that are individually close to the allowable coupling but collectively sum
above
the absolute maximum coupling. Of these paths one of them has a resonate in
the
frequency of interest which to be safe we took care to damp this path while
trying to further isolate the others.
Regards,
-Jory
________________________________
From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
To: steve weir <weirsi@xxxxxxxxxx>; Jory McKinley <jory_mckinley@xxxxxxxxx>
Cc: Istvan Novak <istvan.novak@xxxxxxx>; liuluping 41830
<liuluping@xxxxxxxxxx>;
si-list@xxxxxxxxxxxxx
Sent: Sat, December 25, 2010 1:57:35 PM
Subject: [SI-LIST] Re: Does power/ground pair edege radiation noise really
matter in the EMI test?
This is a lot of discussion about something that is rarely, if ever, a
problem. There are a number of papers published on this topic that show
this.
--------------------------------------------------
From: "steve weir" <weirsi@xxxxxxxxxx>
Sent: Friday, December 24, 2010 11:08 AM
To: "Jory McKinley" <jory_mckinley@xxxxxxxxx>
Cc: "Istvan Novak" <istvan.novak@xxxxxxx>; "liuluping 41830"
<liuluping@xxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Does power/ground pair edege radiation noise really
matter in the EMI test?
> Jory, pretty much with some clarification to point 2: We don't want
> undamped resonances to occur:
>
> 1. At frequencies where there is available energy to excite them and
> either
> 2a. At physical locations where they will couple into circuits such that
> they disturb operation of those circuits.
> 2b. At physical locations where they will couple couple to the outside
> world enough to create emission, and/or susceptibility problems.
>
> With narrow-band circuits we an locate resonances either well above or
> well below ( ferrite beads or etch inductors and decaps ) excitation
> current frequencies. With digital we used to routinely be able to
> locate resonances well above excitation frequencies. Now, as you note,
> that is not so true.
>
> Merry Christmas.
>
>
> Steve
> Jory McKinley wrote:
>> 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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>>
>>
>>
>
>
> --
> Steve Weir
> IPBLOX, LLC
> 150 N. Center St. #211
> Reno, NV 89501
> www.ipblox.com
>
> (775) 299-4236 Business
> (866) 675-4630 Toll-free
> (707) 780-1951 Fax
>
>
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