PCB DESIGN - separating digital/clock/audio ground planes

[Teej212]

is it a necessary precaution to separate ground planes on pcbs containing a digital clock and an audio section? would it be simple enough to have bottom plane clock/sequencer and have the top plane be audio? or should it be separated like digital on one plane and analog on the other? should I take any further precautions?

for what its worth I am working with the electric druid tap tempo chip, a 4017 sequncer and an fv-1 + I/O buffers.

[multi_s]

there are a lot of good app notes on this. i believe the term people usually use is "mixed signal pcb design". i have some saved on my cpu at the office i will try to link them when i get there...

whether or not you actually want to separate the planes has more to do with the layout of the board. what is more important is actually separating analog and digiatal sections (geographically). and having say your supplies in between them, this emulates a "star ground" sort of style you would see in point to point wiring. This way the analog current path stays in the analog area, the digital current path stays in the digital area, there is no interference (in theory), but the entire ground plane might well be one piece in this case. You will find a lot of different opinions but i found most people agreed that this was the best idea. If you cant isolate the analog and digital sections that cleanly, splitting the ground plane might be a good idea to at least be able to force the return currents along a certain path.

in the end, whether or not its absolutely necessary is hard to say with out experimenting, but that is the basic philosophy.

[Teej212]

ok good to know, would definitely love to see those notes. So when you say digital would you lump the fv-1 and the tap tempo chip in the region on the pcb with the buffer and the sequencer in another region? or would it be wiser to separate clock/counter in one section and the audio section in another? or some other combination

[multi_s]

well you can always try google as well.


http://www.ti.com/lit/an/slyt499/slyt499.pdf
http://www.ti.com/lit/an/slyt512/slyt512.pdf

http://www.maximintegrated.com/en/app-n ... vp/id/5450

this one is a bit more about the science
http://www.analog.com/media/en/technica ... 5AN280.pdf

etc

the fv-1 is mixed signal itself. you can look in the above notes if there are things about data converters or other things that would need to connect to both the digital and analog section etc, and treat it similarly.

[Teej212]

thanks, i was planning on googling it when I got back home and on something easier to use than my phone. Ive read before that there isnt a need to have a digital ground and analog ground separate for the fv-1, just unsure if adding a clock will change anything. thanks for you help

[culturejam]

Teej, you might want to check out the digital subforum that was recently set up at Madbean's place:
http://www.madbeanpedals.com/forum/index.php?board=81.0

[Teej212]

culturejam that looks awesome! hopefully a project gets rolling soon so people can get to programming unique effects! but in the mean time Im excited about this pitch sequencer I am working on. just waiting on some packages so I can bread board the sucker

[culturejam]

Feel free to post your project over there as well. All digital is welcome.

[Teej212]

one more question - when separating grounds do they need to be on different sides of the board or can they just have a gap between them?

[multi_s]

you want the ground for a signal running under the signal trace. so the short answer is, both grounds can be on the same layer of the pcb. look at fig 3 in the first link and just imagine both grounds are on the same layer