Hello,
I am designing 6 layer PCB In which Layer 2 is mostly for Ground. I have AGND, DGND, GND in my design.
Can someone help me how can I keep separate them, so I won’t get any noise problem.
Thank you.
Create three separate, non overlapping filled zones on your ground layer. One filled zone set to net AGND, one filled zone to DGND, and one filled zone to GND.
Make sure you actually have a component (a jumper, choke, whatever meets your design requirements) on the schematic that connects them (unless they are supplied separately on a connector…) otherwise if you have them connected by a schematic wire they won’t show as separate nets when you export the netlist.
The current advice is not to separate planes.
The reason is that it is quite easy to create bad signal return paths.
This creates a slot antenna that radiates and receives noise.
It also contributes to ground bounce.
A small remark: The current returns on the path of least impedance (not necessary the path of least resistance)
This effect is measurable for signal frequencies >= 10kHz
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It’s simply not that simple for anything but the most trivial designs.
For the most part follow @Rene_Poschl’s advice above paying particular attention to AC signal return paths. It’s not just a matter of frequency, digital signals usually have fast rise/fall times, this is just as important as frequency. Not only can this be a source of EMI it can also affect the timing of signals since a signals timing not only depends on the characteristics of the track carrying the signal but also the return path.
If you do have signals crossing the split between ground planes then you need to consider having stitching capacitors to bridge the gap and provide an AC return path. Split planes should only connect at one place, that is they should have only one low resistance DC connection, usually at the source (ie. power supply or power connector). This connection is usually in the form of an inductor such as a ferrite bead with appropriate power handling.
Also you need to pay special attention to any planes such as power planes on other layers that overlap your ground planes. Having a digital power plane overlapping your AGND plane will capacitively couple the planes giving the noise from the digital power plane a path to your AGND plane defeating the purpose of having split ground planes.
Splitting ground planes can be tricky business, you can end up with a board that doesn’t work as well as one with just one solid ground plane.
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Hello,
Thank you for the reply, Yes, I created layer2 as ground without splitting ground @1.21Gigawatts and @Rene_Poschl Thanks for the information.