Ken, My dilemna is regarding a mixed-signal design with an FPGA interfacing to 16-bit ADCs and DACs. Would I simply be better off not isolating the analog ground (which will be connected at some point anyway) and put barriers on the signal layers so I don't have any high-speed signals next to the precious analog? With good placement the two worlds are partitioned with the exception of the serial data/control between the FPGA and the analog converters. Here's where the temptation is to spilt the ground planes to block switching currents from entering the analog ground. Pat -----Original Message----- From: Ken Cantrell [mailto:Ken.Cantrell@xxxxxxxxxxx] Sent: Friday, February 01, 2002 10:10 AM To: psharkey@xxxxxxxxxxx; Si-List@Freelists. Org Subject: RE: [SI-LIST] Split Plane Routing Pat, Other than NEVER(personal opinion)splitting the ground plane: 1 - S1 2 - pwr1 (lowest voltage) 3 - S2 4 - gnd 5 - pwr2 (highest voltage) 6 - S3 7 - gnd 8 - S4 would work. If emissions are still an issue, flood the top and bottom. That may not fix your emissions, but it will reduce it. The way the board is tied to the chassis is just as critical as the board emissions themselves. There are times when you have to split the ground plane, but you should, in general, resist any push to do this. If it is a "must do", then minimize the number of traces crossing the split, and confine the type of traces to slow and/or aperiodic signals. Ken -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Pat Sharkey Sent: Friday, February 01, 2002 7:10 AM To: Si-List@Freelists. Org Subject: [SI-LIST] Split Plane Routing Hello all, Given the following stackup with planes split in different areas - 1 - S1 2 - GND (SPLIT 1) 3 - S2 4 - GND(SPLIT 2) 5 - POWER(SPLIT 3) 6 - S3 7 - GND (SPLIT 4) 8 - S4. For a signal which originates on layer 8, should the signal only be routed on layers 6 & 8? Or, can layers 1 and 3 also be used to cross a plane split on layer 7, assuming layers 2 and 4 are not split in the same place (z axis)? Thanks in advance, Pat ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list 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 or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list 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