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 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu