[SI-LIST] Re: Power Plane resonance analysis

  • From: Ihsan Erdin <erdinih@xxxxxxxxx>
  • To: steve weir <weirsi@xxxxxxxxxx>
  • Date: Fri, 28 Aug 2009 07:11:06 -0400

That's correct. A parallel plate power/ground plane pair is basically
a nonuniform transmission line for which both C and L are
area-dependent. The phase velocity is simply c0/eR for an ideal
component between those two planes. In actual case, however, the
mounting inductance of the component may vary the velocity
significantly.

Regards.

Ihsan

On Thu, Aug 27, 2009 at 6:38 PM, steve weir<weirsi@xxxxxxxxxx> wrote:
> Propagation velocity depends only on eR.
>
> Steve.
> Aleksandr Oysgelt wrote:
>> How do you figure out propagation delay through planes?  Is it sqrt(L/C) so
>> L is about 32pH/mil of separation (sheet inductance) but what is C (which is
>> area dependent - no concept of "sheet capacitance")?
>> Thank you
>> Aleks
>>
>> On Thu, Aug 27, 2009 at 5:25 AM, Istvan Novak <istvan.novak@xxxxxxx> wrote:
>>
>>
>>> 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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>>
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>
>
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