[SI-LIST] Re: Leaving, then re-entering a reference plane

Don,
If you do go down the path of simulating the split and looking at 
what-ifs, there is a parameterized HFSS deck for simulating split planes 
posted here:
http://www.hfss-forum.com/viewtopic.php?f=19&t=6
If you have any questions about the deck, feel free to contact me 
directly or post them on the forum link above.
Thanks,
Jason Miller

Scott McMorrow wrote:
> Don
>
> Unfortunately, you have a classical non-localizable split plane problem 
> that is not possible to understand with intuition alone.  By 
> non-localizable, I mean that the EM fields are not confined to a small 
> region that can be easily analyzed.  Non-localizable problems occur when 
> there are plane excitations due to vias penetrating planes, or traces 
> crossing plane splits.  At the discontinuities, the signals will inject 
> a parallel plate mode wave into the split core power plane, which will 
> cause excitation at the 1st, 3rd and 5th harmonics of the incident bit 
> pattern.  When the pattern spectrum (and it's harmonics) aligns with a 
> power plane resonance, a standing wave pattern will develop that will 
> increase the power system noise, along with the signaling noise, jitter 
> and crosstalk. 
>
> What you will need to look for is the parallel resonant frequency of the 
> power plane, that is, the resonant frequency of the bypass capacitor 
> mounting inductance, and the plane capacitance.  However, since there is 
> no ground plane adjacent to the split power plane, the impedance will 
> most likely be high on the average, and exceedingly high at resonance.  
> This has the potential of being a very bad thing, and extremely 
> sensitive to process variations of the PCB and the capacitors being used. 
>
> You have 3 possible courses of action, in order of best to worst.
>
> 1) Redesign to remove the split.
> 2) Simulate it in a planar fullwave solver like Ansoft SIWave.
> 3) Build it and measure the signal and power system.  A spectrum 
> analyzer would be very useful to determine where the resonant peaks 
> occur, and whether they will cause meaningful noise, crosstalk, or jitter.
>
>
> regards,
>
> Scott
>
>   
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