FreeLists / si-list / [SI-LIST] Re: power plane spacing

["Ye, Xiaoning" <xiaoning.ye@xxxxxxxxx>]

Smaller power/ground plane spacing is beneficial for EMI. Actually, the
raidate EMI (resulting from the fringing field of power-bus structure) is
approximately proportional to this spacing (which corresponds well with
microstrip antenna theory). Results of measurements and simulations both
support this conclusion.

Here are two references:

"An investigation of PCB radiated emissions from simultaneous switching
noise" 1999 IEEE International Symposium on Electromagnetic Compatibility, ,
Volume: 2 , 1999 Page(s): 893 -898 vol.2
"The EMI benefits of ground plane stitching in multi-layer power bus stacks"
IEEE International Symposium on Electromagnetic Compatibility, 2000.,
Volume: 2 , 2000 Page(s): 833 -838 vol.2

---Xiaoning

_________________________
Xiaoning Ye
Intel Enterprise Architecture Labs (EAL)



-----Original Message-----
From: Chris Padilla [mailto:cpad@xxxxxxxxx]
Sent: Wednesday, July 11, 2001 4:03 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: power plane spacing



...ah, which reduces current loop area which can help mitigate EMI 
radiation in the >250 MHz spectrum.

Further, it is more a LOW inductance capacitor that has a wide bandwidth in 
which to operate as a capacitor...if that is what you mean by "high 
performance."

----->Chris

>The small spacing has nothing to do with EMI.  It has to do with creating a
>large value, high performance capacitor to supply switching currents.
>
>Lee
>
>DORIN OPREA wrote:
>
> > Hi everyone,
> >
> > In high speed design we often use the split planes on a power layer. The
> > spacing between the digital planes is correlated with the distance
> > between the power layer to the ground layer. In general we have 50 mil
> > spacing. It just happen to run into a different opinion which recommends
> > a very small spacing due to the slot antenna effect (the gap between the
> > planes) that allows the eddy currents to radiate. A small spacing may
> > couple noise into the low power supply (1.5V or 1.8V).
> > How critical is this radiation effect versus noise coupling between the
> > two power distribution systems ?
> > What is the practice out there ?
> >
> > Thanks very much for you guys always being there,
> > Dorin

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