[SI-LIST] Re: Power Plane resonance analysis
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Aleksandr Oysgelt <aleks@xxxxxxxxxxxxxxxxxx>
- Date: Thu, 27 Aug 2009 15:38:09 -0700
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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