[SI-LIST] Re: Routing Signals Between PWB Layers - Part 2
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: lnima@xxxxxxxxxx
- Date: Thu, 04 May 2006 13:04:30 -0400
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Scott McMorrow
Teraspeed Consulting Group LLC
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(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
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Nima Lotfi wrote:
> Istvan,
>
> I'm looking for a tool to simulate board resonance. Did you use
> simulation software to confirm the frequency of modal resonance of the
> PCB planes? If so can tell me what tool you've used.
>
> Thanks,=20
> ______________________=20
> Nima Lotfi, P. Eng=20
> Digital Hardware Design Engineer=20
> Nortel
>
>
> 758-7786 ESN=20
> (403) 769-7786 Direct=20
> (403) 769-5350 Fax=20
> LNima@xxxxxxxxxxxxxxxxxx=20
>
>
>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx
>>
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
>
>> On Behalf Of Istvan Novak
>> Sent: Thursday, May 04, 2006 7:10 AM
>> To: GStokes@xxxxxxxxx
>> Cc: SI-List
>> Subject: [SI-LIST] Re: Routing Signals Between PWB Layers - Part 2
>> =20
>> Geoff, Doug,
>> =20
>> This example nicely shows the importance of proper power distribution
>> design.
>> =20
>> The emission peaks correspond to the modal resonances of the PCB
>>
> planes.
>
>> As Doug points out in the article, moving the planes closer would
>>
> reduce
>
>> the
>> emission about proportionally. However, if one wants to stay with a
>> four-layer
>> construction, reducing the plane separation is not a viable solution:
>>
> it
>
>> would
>> either result in an unmanageably thin board, or if we add the
>>
> tickhness
>
>> back to
>> the top/bottom dielectrics, in a dramatically reduced routing density.
>> =20
>> Nearby grounding vias would help, but in practical cases the two
>>
> planes
>
>> are at
>> different DC potentials, so it must be a bypass capacitor rather than
>>
> a
>
>> stitching
>> via. A single bypass capacitor will do little in the hundreds of MHz
>> frequency range,
>> even if it serves only one signal. Also, if we have wide busses
>>
> instead
>
>> of a single
>> trace, trying to provide a return path locally to all of the layer
>> transitions becomes
>> much harder to implement.
>> =20
>> A more realistic and straightforward solution is to design the
>> power-distribution
>> network in such a way that it does not exhibit large resonances. In
>> multi-layer
>> boards, where we may also have ground-ground planes creating such
>> cavities, the
>> solution is stitching vias, but not necessarily near the layer
>> transitions. We would
>> just need to make sure that the large resonating cavity is broken up
>>
> to
>
>> sufficiently
>> small blocks such that the lowest resonance frequency is safely above
>> the highest
>> frequency of excitation.
>> =20
>> Regards,
>> =20
>> Istvan Novak
>> SUN Microsystems
>> =20
>> =20
>> =20
>> Geoff Stokes wrote:
>> =20
>>
>>> Hi Doug
>>>
>>> In this experiment, you appear to have no plane vias adjacent to the
>>> signal vias. What would happen if a few plane vias were added around
>>> the transitions and fairly close by?
>>>
>>> Geoff Stokes
>>> Systems Engineer
>>> Zetex Semiconductors plc
>>> Zetex Technology Park
>>> Chadderton
>>> Oldham
>>> OL9 9LL
>>> UK
>>> =3D20
>>> +44-161-622-4857
>>> www.zetex.com
>>> www.zetex.cn
>>> =3D20
>>>
>>> =3D20
>>> -----Original Message-----
>>> From: si-list-bounce@xxxxxxxxxxxxx
>>>
> [mailto:si-list-bounce@xxxxxxxxxxxxx]
>
>>> On Behalf Of Doug Smith
>>> Sent: 03 May 2006 21:41
>>> To: SI-List
>>> Subject: [SI-LIST] Routing Signals Between PWB Layers - Part 2
>>>
>>> Hi All,
>>>
>>> I have been writing and recording again and have posted part 2 of
>>>
> my=3D20
>
>>> article on signals that change layers in a PWB.
>>>
>>> Abstract: Printed wiring board, PWB, signal paths must often
>>>
> change=3D20
>
>>> layers in a board stackup. Under some conditions this can cause=3D20
>>> problems. An emissions example is used to illustrate the
>>>
> conditions=3D20
>
>>> where changing layers can cause problems.
>>>
>>> The link to the article is the picture of the emissions plot at
>>>
> the=3D20
>
>>> bottom of the home page at http://emcesd.com .
>>>
>>> There is also an audio discussion of this article on my podcast
>>>
> site:=3D20
>
>>> http://emcesd-podcast.com where the direct link to the article is:
>>>
>>> http://emcesd-podcast.com/2006/may/2006-0503.mp3
>>>
>>> Can't download mp3 files? Download the following instead:
>>>
>>> http://emcesd-podcast.com/2006/may/2006-0503.dcs
>>>
>>> After download, change the extension from .dcs to .mp3 and the
>>>
> file=3D20
>
>>> will then be able to play on most computers. Since the last =
>>>
> HFNews=3D20
>
>>> there have been two new podcasts posted.
>>>
>>> Doug
>>> --=3D20
>>> -------------------------------------------------------
>>> ___ _ Doug Smith
>>> \ / ) P.O. Box 1457
>>> =3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D=3D3D Los =
>>>
> Gatos, CA 95031-1457
>
>>> _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
>>> / /\ \ ] / /\ \ Mobile: 408-858-4528
>>> | q-----( ) | o | Email: doug@xxxxxxxxxx
>>> \ _ / ] \ _ / Website: http://www.dsmith.org
>>> -------------------------------------------------------
>>>
>>>
>>>
>>>
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