What to consider when implementing a solid ground plane for a 6 layer stack up?

Hello,

For a mixed system wireless system design based on a mixed signal chipset the suggestion is to use a solid ground plane for analog and digital grounds. What considerations has to be considered/implemented in doing so for a six layer stack up

Re: Solid Ground plane

The most important thing to do is to keep the analog and digital grounds separated. Tie them together at one point.
In this way the noise from the digital ground is not disturbing your analog devices.

Re: Solid Ground plane

Hi ...

Some considerations you need to keep in mind:

- What the frequency of analog parts?
- Is there any audio part ?
- What the frequency, rise and fall times of digital ?

Keep audio plane separated of others, in most cases some switching noise are audible and they could be coupled by ground. In this case try to use inductors or beads.
In a six layer board keep grounding in adjacent layer of your most critical signals.
In some cases no matter so far your ground planes are separed, some signals are carried from one ground to other by signal tracks crossing both planes.

Good luck ...

Re: Solid Ground plane

I am using the following 6 layer stackup for a wireless system module design based on a reference chipset in 2.5 Ghz and the layout recomendation is to have a solid ground plane as ground for digital,analog sections

TOP 0.05 mm copper foil+copper plating
DIELECTRIC 0.1016 mm 4 mil Core
LAY2 0.035 mm 1 oz Solid Ground
DIELECTRIC 0.1016 mm 4 mil PrePreg
LAY3 0.035 mm 1 oz Digital Signals
DIELECTRIC 0.3556 mm 14 mil Core
LAY4 0.035 mm 1 oz Digital Signals
DIELECTRIC 0.1016 mm 4 mil PrePreg
LAY5 0.035 mm 1 oz Power Plane
DIELECTRIC 0.1016 mm 4 mil Core
BOT 0.05 mm copper foil+copper plating Ground
Total 1.002 mm
FR4 Material used is ISOLA 370HR

I have taken care of the following.
Single sided component placement on top layer
No Digital routing in place of RF Routing
Individual grounding of RF, Digital grounds by vias to Solid ground plane on layer 2
RF,Crystal routing in top layer
Critical Digital routing in Layer 3(SPI,USB)
Non critical digital routing in Layer 4(UART)
Analog,Digital power planes in Layer 5
Ground in Layer 6
Taken care that Layer 4 signals doesnt cross power splits.

I dont understand what is tying of analog,digital grounds at one common point when the recommendation is to use a solid ground plane for analog/digital.

Is any other factors to be considered for a solid ground plane as reference ground plane