Gene, You've left out some relevant information (e.g. what/where are your external analog/digital connections to the board, how many layers do you have available, how many mixed signal devices do you have, ...). Nevertheless, it is pretty safe to say that you should not be gapping your ground plane in this situation. If the board is mostly digital, provide a solid digital current return plane and route your audio analog current returns on a different layer. Your audio and digital return conductors should only be connected at one place (near your ADC). Be sure there are not sneak paths through externally attached devices or the power supply. You say that creating a single-point connection between the analog and digital areas is unlikely given the topology. That may be true if you try to keep both analog and digital current returns on the same layer, but it should not be too difficult if you route them on different layers. You can always cut up your power layer under the analog sections of the board if you need to. Maintaining control of your audio frequency current paths should be a top priority in your layout. Todd Hubing Clemson University http://www.cvel.clemson.edu -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Gene Glick Sent: Monday, June 21, 2010 11:20 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] analog and digital partitioning hi all, I am struggling with some partitioning decisions, maybe you can help. This card has an analog section (audio), digital (uP running around 200 MHz, SDRAM, etc.), mixed (ADC, DAC). For the most part, the analog and digital sections are completely separate. The mixed signal devices straddle the partition. Some digital signals pass over the boundary, but are psuedo-static control lines. One clock signal (1 MHz) also crosses the boundary. Creating a single-point connection between analog area and digital area is very unlikely given the topology. I wanted to moat around the analog sections, but effectively will wind up with slots in the ground plane. So the question is, how bad is it to have slots in the ground plane? Are slots acceptable if no return currents or eddies flow around them? Somehow, I don't believe it possible to be 100% certain of this. An alternative, is to have one solid ground plane, keeping the signals routed such that no return currents flow where they should not. But I am concerned with keeping the audio noise floor at a very low level. thanks gene ------------------------------------------------------------------ ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu