Ground Planes? - RF Cafe Forums
Post subject: Ground Planes? Posted: Mon Jan 23, 2006
Hi all! I was reading about ground planes and it seems
like the majority of the advice points to a design where two ground
planes are created for analog and digital signals and only connect
them at one point near the power supply. But I was reading some
more articles and noticed, this:
"A number of different ground
plane strategies can be adopted for a radio product PCB. There is
no unique answer to the best strategy for a given type of product.
Some people are great advocates of split ground planes for analogue,
digital, radio or audio circuits. Experience on a number of radio
products at Plextek has shown that a single low impedance ground
plane for all parts of the circuit is usually a good starting point.
Often attempts to split the ground planes causes more problems than
it solves. Careful consideration of the flow of currents throughout
the product is essential to minimise digital interference with audio
and radio circuits. Given the proliferation in the use of DSP and
microprocessors in radio products this is a very significant issue."
Can anyone comment from experience? Thanks!
Post subject: Ground planesPosted: Tue Jan 24,
2006 3:30 pm
The major issue is how much non-DC current flows
in the ground region.
I've had good results both ways, but
there are a couple of non-obvious (to most people) things to watch
1. Ground loops. If using separate ground planes,
proper ("star") grounding becomes more significant. Ground loops
can be hard to avoid anyway, but can be critical for small-signal
applications requiring low noise pickup.
2. Proper bypassing.
This reduces the difference between the two configurations. There
need to be both small, high-self-resonant-frequency capacitors at
the point of power use, the power plane/ground plane capacitance,
and a bulk capacitor as well. There's a lot of material about this
on the web - unfortunately, not all of it is correct. Watch out
for unwanted resonances.
Basically, keep an eye on where
the current is flowing.
Post subject: Posted: Wed Jan 25, 2006 3:05 pm
Joined: Mon Jun 27, 2005 2:02 pm
The issue that
you raised is a very acute one. I had the same concerns on my last
PCB layout, which was for a large Mixed-Signal board with close
to 2000 components and included high-speed Digital sections and
RF sections up to 400MHz. What I did is using separate ground planes
for the Analogue/RF sections and digital sections and added optional
resistors at the schematic to connect between these planes. I connected
via holes from the different GND planes to the top layer and making
an option for connection between the planes through these resistors
Eventually I connected between the planes
through the resistors. Indeed, there is no one-way solution to this
issue as the 2nd guest mentioned in his reply. Therefore, you should
make an option in your layout to cover both options.
Post subject: Posted: Wed Jan 25,
2006 5:37 pm
Thanks for the info!
I've seen that term
star grounding before. Is that similar to starpoint ground? If so,
can someone kindly explain this? I am not familiar. Thanks!
Post subject: Posted: Wed Jan 25, 2006
Joined: Mon Jun 27, 2005 2:02
Here is a link for you with relevant information:
Additional information can be found by Google!
subject: Posted: Sat Apr 01, 2006 5:13 pm
Joined: Thu Mar 23, 2006 4:18 am
you might wanna
have a look at the high speed PCB layout seminar by analog devices
http://www.analog.com/en/content/0%2C28 ... %2C00.html
scroll down for this seminar.