Ground Planes? - RF Cafe Forums
Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: Ground Planes? Posted: Mon Jan 23, 2006 5:15 pm
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 out for:
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 if neccessary.
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
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 5:57 pm
Joined: Mon Jun 27, 2005 2:02 pm
Here is a link for you with relevant information:
Additional information can be found by Google!
Post subject: Posted: Sat Apr 01, 2006 5:13 pm
Mar 23, 2006 4:18 am
you might wanna have a look at the high speed PCB layout seminar by analog
http://www.analog.com/en/content/0%2C28 ... %2C00.html
scroll down for this seminar.