[SI-LIST] Re: Power Plane resonance analysis
- From: Istvan Novak <istvan.novak@xxxxxxx>
- To: "Haller, Robert" <rhaller@xxxxxxxxxxxxx>
- Date: Fri, 28 Aug 2009 20:32:28 -0400
Bob,
Not sure I follow your question. Are you asking whether we could see
plane resonances on a spectrum analyzer connected to a pick up loop,
placed near to a plane pair while we excite the plane pair? Or are you
asking how we could reduce the resonance simply by experimentation, like
finding out where to place what kind of capacitor?
If the first, yes, it is somewhat doable, with the following
limitations. You really have to have just a laminate pair, not layers
inside a multi-layer PCB. Moreover, such structures, no matter how you
try to excite it, will always create a field representing not only the
structure but also the excitation circuitry (cable, etc). But most
importantly, it is very challenging to excite a hugely varying impedance
with a constant amplitude signal. So interpreting the result would be
tricky.
Regards,
Istvan Novak
SUN Microsystems
If the second,
Haller, Robert wrote:
> Istvan,
> If you suspected a Plane resonance in a unusual shape, and you wanted
> to experimentally fix it how would you do that ?
>
> For Example, let's say you had a shape similar to an inductive pickup (square
> loop), and you wanted to experimental eliminate the resonance how could you
> accomplish that ?
> If you fixture up a spectrum analyzer to the Plane and excited it, would you
> expect to see the resonances show up as spurs in the power spectrum at the
> resonant frequency(s)?
>
>
> Regards
> Bob Haller
> Enterasys Networks
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Istvan Novak
> Sent: Thursday, August 27, 2009 8:26 AM
> To: Sandhya I. M.
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Power Plane resonance analysis
>
> Hi San,
>
> If you have the good luck to have rectangular plane shapes, you can
> simply calculate the
> modal resonance peak frequencies from the propagation delay along each
> of the two sides
> of the rectangle. 1/(2*tpd) gives you the lowest resonance peak, and
> you will get all of
> the harmonics, so it becomes a double infinite series. On typical PCB
> dimensions today,
> the first five or ten resonance peaks matter in self impedance; the
> higher-order modes
> will tend to blend together into an inductive slope.
>
> For more complex shapes the modal resonance frequencies need to be
> calculated by
> an appropriate software. You can go from simple and low-cost tools like
> EZPlane
> (http://www.ems-plus.com/ezpowerplane.html) to more sophisticated tools
> like
> Sphinx (http://www.e-systemdesign.com/products.aspx) to high-end tools such
> as Ansoft SiWave or HFSS. For HFSS and correlation on power planes, you can
> check out the Unofficial HFSS User forum (http://www.hfss-forum.com/).
>
> To make sure that resonances do not create a problem, best and cheapest
> defense
> is to make sure you dont excite them. You can do this by creating a
> stackup to
> minimize signal-return currents going through unrelated power-ground
> cavities.
> To reduce the resonances themselves, you can either sprinkle the planes
> with many
> capacitors, match the planes or use thin laminates, or a combination of
> these. If
> you sprinkle the planes in the old-fashioned brute-force manner, you
> could use the
> same capacitance value, say 0.1uF or 1uF. Key is minimizing the inductance
> in the capacitor connections because with the cumulative inductance of
> all capacitors
> on the plane you want to stay below a couple of percents of the plane's
> inductance.
> You can read more on these design options at
> http://www.electrical-integrity.com/,
> go to Paper download. In the Tool download section you can also find
> simple
> illustration tools for plane resonances.
>
> For measurement options, you can look at the paper "Frequency Domain Power
> Distribution Measurements - An Overview" from DesignCon 2003 East, Boston,
> MA, June 23-25, 2003. You will find it at the site above. For more
> details and
> tips, you can look at the book Frequency-Domain Characterization of Power
> Distribution Networks, Artech House, 2007.
>
> Regards,
>
> Istvan Novak
> SUN Microsystems
>
>
>
> Sandhya I. M. wrote:
>
>> Hi SI experts,
>>
>> If any one can help me in doing PCB Power Plane resonance analysis by
>> sharing documents or by explaining how it occurs.
>>
>> What are the causes of PCB Power Plane resonance analysis
>> How can we measure resonant frequency
>> How decoupling caps helps in suppressing resoinance in planes.
>> What are the factors we should consider while doing resonance analysis.
>>
>> Thank you
>>
>> Regards
>> san
>>
>>
>>
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