It would be interesting to know what the noise levels are with and without
the splits and how they were measured.
How do we know they were really effective?
The noise floor on my scope is around 20 mV which can be made lower by
reducing the bandwidth.
On Wed, Jan 18, 2017 at 6:16 AM, Istvan Novak <istvan.novak@xxxxxxxxxxx>
wrote:
Ken, Lee,
Yes, what I meant was that in mixed-signal boards and on some boards
where naturally very noisy circuits (like high-current DC-DC converters)
have to coexist with sensitive circuits, like SerDes, PLLs, etc,
splitting the ground plane between the domains can improve the isolation
and thus improves performance, as long as we make sure that we dont
create SI and/or EMI problems by crossing the splits with signals that
otherwise need a solid reference. For instance, when I open up my USB
powered 100Ms/s oscilloscope, its PCB clearly has moats, cuts and slots
on the planes (including the GND or reference planes) between the ADC
input section and the high-swing arbitrary waveform generator DAC circuit.
Regards,
Istvan Novak
Oracle
On 1/17/2017 6:32 PM, Ken Wyatt wrote:
Argh, my apologies Istvan. I indeed misread your description, as pointedout by two of our colleagues, Vinu and Bert.
Yes, I agree that there are cases where planes may be split for variousreasons - mainly isolation, etc. We just need to be sure not to cross that
split with clock or other high-speed traces.
questions related to EMC or EMI troubleshooting - at no obligation. I'm
Crawling back into the woodworkââ¬Â¦ :-)
Cheers, Ken
_______________________
I'm here to help you succeed! Feel free to call or email with any
always happy to help!
http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/>
Kenneth Wyatt
Wyatt Technical Services LLC
56 Aspen Dr.
Woodland Park, CO 80863
Phone: (719) 310-5418
Email Me! <mailto:ken@xxxxxxxxxxxxxxxx> | Web Site <
The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog>Newsletter/Newsletter.html>
Subscribe to Newsletter <http://www.emc-seminars.com/
Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt>especially in very dense designs. You mentioned some cases where splits
On Jan 17, 2017, at 1:05 PM, Ken Wyatt <ken@xxxxxxxxxxxxxxxx> wrote:
Hi Istvan,
I would have to agree there can be many trade-offs in board designs -
were OK and Iââ¬â¢d be interested in any additional specific conditions
where
splitting the return (or reference) plane is OK from a SI or EMI point of
view, or can even make it better, as you point out.
say) clocks or other digital signals cross a gap in the return plane,
In general, my experience has been in cases where high speed (>100 kHz,
common mode harmonic currents are produced, which can create not only
crosstalk to victim traces, but worse, these currents can flow out the
outside of I/O cable shields, creating the potential for radiated
emissions. I understand there are situations where this canââ¬â¢t be helped
and I do believe there are cases where this doesnââ¬â¢t matter much.
https://youtu.be/L44lTnQgv-o
I created a short video demonstration of this effect.
questions related to EMC or EMI troubleshooting - at no obligation. I'm
Cheers, Ken
_______________________
I'm here to help you succeed! Feel free to call or email with any
always happy to help!
http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/>
Kenneth Wyatt
Wyatt Technical Services LLC
56 Aspen Dr.
Woodland Park, CO 80863
Phone: (719) 310-5418
Email Me! <mailto:ken@xxxxxxxxxxxxxxxx> | Web Site <
Newsletter/Newsletter.html>The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog>
Subscribe to Newsletter <http://www.emc-seminars.com/
wrote:Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt>
On Jan 16, 2017, at 9:05 PM, Istvan Novak <istvan.novak@xxxxxxxxxxx>
would
Lee,
Nice article and I agree with most of what you say, though I still
betweennot use extreme phrases, like on page 6 you say "Splitting a ground
plane destroys its integrity as an ultralow impedance connection
sometimesall of the components in a circuit and should never be done." I agree
that the reference (ground) plane is very important and we should make
sure it can serve its purpose properly. However, in complex and high
density designs there are several conflicting requirements and
makemaking careful splits on the ground planes are not only OK, it will
wethe product outright better. There are occasions, for instance, when
Martinneed to equalize and optimize the DC drop on planes and in addition to
optimizing the placement of components, we can also help by splitting
the planes, power and/or reference planes. If signal traces are
naturally routed alongside the split without the need to cross it, the
signaling will be OK. There are real, working products with split
ground planes.
Regards,
Istvan Novak
Oracle
On 1/16/2017 6:53 PM, Lee Ritchey wrote:
A few weeks ago we had a prolonged exchange on what ground is. With
section onRowe, we did an article that appeared on the UBM site with this URL.
http://ubm.io/2ikEDat
I wrote another article that includes this as well as an expanded
article isEMI and ground and Faraday Cages and how they contain EMI. That
the firstnow posted on the Speeding Edge web site, www.speedingedge.com
<http://www.speedingedge.com> for any who want to go beyond what
topic.article covered.
Hope both of these help clear up some of the confusion around this
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See you all at DesignCon in Santa Clara at the end of the month.
By the way, I am planting flowers in my ground this month!
Lee Ritchey
Speeding Edge
P.O. Box 2194
Glen Ellen, CA
95442
707-568-3983
I just used the energy it takes
To get mad and wrote some blues.
Count Basie
Or:
Worry is like a rocking chair,
It keeps you busy but.
It doesn't get you anywhere.
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