Hello *,
basically I agree on the theoretical statements that have been given.
But an Ethernet Port is not a rare interface, but nearly on each design.
And this is one of the occasions where I would agree to the design
guides to separate "External chassis Ground" coming from the Ethernet
cable shield vs. Internal Ground (and connect only via a DC block
capacitor).
But I do not think, that it is possible / useful to have this Ethernet
GND at the IO shield separated from all other IO Shield GND.
Or is the groups advise also to connect Ethernet shield directly to
internal GND and to all other small range interfaces shields like USB ?
At least at the IO panel all these Grounds are usually connected together.
Assuming I separated Ethernet GND at the IO Panel .. then I need to to
have all other Cable shields/GND also on this separated shield.
Otherwise I need a separate Connector panel just for Ethernet, right ?
and this is something I usually do not see.
Maybe my memory is wrong I have to get back to the Ethernet standard and
re-read the design guides I thought to remember.
Any Feedback is welcome!
Hermann
Our next Events:
visit us on "embedded world 2017"
14.03-16.03.2017 - Hall A2, Booth 651
EKH - EyeKnowHow
Signal Quality - Made in Bavaria
Hermann Ruckerbauer
www.EyeKnowHow.de
Hermann.Ruckerbauer@xxxxxxxxxxxxx
Itzlinger Strasse 21a
94469 Deggendorf
Tel.: +49 (0)991 / 29 69 29 05
Mobile: +49 (0)176 / 787 787 77
Fax: +49 (0)3212 / 121 9008
Am 05.12.2016 um 01:58 schrieb Ken Wyatt:
Hi Sudeep,
I have to agree with Doug and Lee when it comes to multiple ground
references. In addition to their points, Iâd like to mention that the
concept of chassis (or any other ground reference) as a ânoise sinkâ is
erroneous. All currents flow in continuous closed loops - from source to load
and back to the source. This includes noise currents created due to various
factors.
Despite our current use of solid return planes (a good thing), the fact they
include minute impedance between any two points allows coupled noise currents
to develop small voltage drops. The concept of a âground referenceâ is
confusing because âzeroâ volts only exists at the location you place the
negative lead of a voltmeter.
Because of the above physics, the other important point is that separate
digital and analog planes (two metallic structures) are likely to develop a
high frequency voltage drop between them, which can then radiate as a dipole
antenna, potentially causing radiated emissions failures.
To get back to the original question, I also fail to see any reason to
connect separate reference planes together using a capacitor. Itâs
important to define specific return paths for all currents, including noise
currents. Adding such a capacitor may create an irregular current path,
depending on frequency and where placed.
Iâd recommend reading Todd Hubingâs excellent articles on PC board design
at http://www.cvel.clemson.edu/emc/index.html. In addition, I can highly ;
recommend Elya Joffe and Kai-Sang Lockâs book, Grounds For Grounding.
https://www.amazon.com/Grounds-Grounding-Circuit-System-Handbook/dp/0471660086/ref=mt_hardcover?_encoding=UTF8&me
I hope this helps clear up some misconceptions.
Ken
_______________________
I'm here to help you succeed! Feel free to call or email with any questions
related to EMC or EMI troubleshooting - at no obligation. I'm always happy to
help!
Kenneth Wyatt
Wyatt Technical Services LLC
56 Aspen Dr.
Woodland Park, CO 80863
Phone: (719) 310-5418
Email Me! <mailto:ken@xxxxxxxxxxxxxxxx> | Web Site
<http://www.emc-seminars.com/> | Blog <http://design-4-emc.com/>
The EMC Blog (EDN) <http://www.edn.com/blog/The-EMC-Blog>
Subscribe to Newsletter
<http://www.emc-seminars.com/Newsletter/Newsletter.html>
Connect with me on LinkedIn <http://www.linkedin.com/in/kennethwyatt>
On Dec 4, 2016, at 5:04 PM, Doug Smith <doug@xxxxxxxxxx> wrote:
HI All,
Although there are (very rarely) reasons why more than one ground
should be used, having separate analog, digital, and chassis grounds
are usually a prescription for disaster in the field and during
compliance testing. You should never separate grounds unless you can
prove you must do so beforehand (not enough to just say you need it,
you must prove you do to avoid problems) and if you do, then you must
be extremely careful that you do not cause other problems. It is rare
that I have seen a design that was careful enough. ESD problems are one
likely result.
Doug
On Sun, 4 Dec 2016 12:22:16 +0530, sudeep sharma <sud22001@xxxxxxxxx> wrote:
Hi Boris,
Say for example in our PCB if we have analog gnd, digital ground and------------------------------------------------------------------
chassis ground and we are going to place this pcb in a chassis ( chassis
body forms chassis gnd).My understanding would be chassis acts as sink for
the noise. So if we r connecting a cap b/w say Dgnd and chassis gnd. In
this scenario, the noise in the Dgnd will get bypassed to the immediate
chassis gnd ( provides least impedance path for the noise generated from
Dgnd), instead of allowing this noise to the other part of the digital or
analog modules present in this PCB. Pls correct me if I'm wrong .
Thanks& Regards
Sudeep
On Dec 4, 2016 02:35, "Boris Bakshan" <bbakshan@xxxxxxxxx> wrote:
Hi all,
This is a very good discussion we have here. However, I stil haven't
figured out if connecting caps between chassis ground and DGND is a good
practice. Bert Simonovich pointed out hat some designers do that but what
would be the main reason for doing so and what is the merit vs. having one
solid DGND ?
On Nov 29, 2016 00:32, "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx> wrote:
Your definition of ground is correct. Where one hooks one side of ameter
or scope when measuring a voltage.a
I am writing an article on the concept of ground that should clear all of
this up. It will appear on line sometime before DesignCon.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Loyer, Jeff (Redacted sender "jwloyer" for DMARC)
Sent: Monday, November 28, 2016 1:23 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Caps between "isolated grounds"?
Here's what I've concluded, for now...
Regarding the original question, I think the caps were placed between
grounds to allow isolating a ground if a problem arose. I doubt this is
good design practice. Another possibility is that in theory, you might"ground"
want
to have a cap between chassis ground and the ground shield of a very long
wire between two systems, but I haven't found a spec. (for long cables)
that
accommodates that kind of shielding so think it's a moot point. I think
having capacitors between grounds is an indication that someone doesn't
know
what they're doing.
Sorry to disagree, but I'll always have a "GND" symbol in my schematics,
even if I'm designing a satellite. For most signals, it's what I'm going
to
hook my ground lead to when measuring voltages. I know the name's not
perfect, but it beats whatever's in 2nd place. For earth system safety
issues, I might have "earth" to handle lightning strikes, and might also
have a "GND" (uninsulated, or green wire) to ensure a return path for
chafed
cables that short to metal (to force a circuit breaker to pop).
Thanks for the thoughts,
Jeff Loyer
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Smith, Larry
Sent: Thursday, November 17, 2016 11:59 AM
To: martin.rowe@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Caps between "isolated grounds"?
I have to go with Bruce on this one. We should eliminate the word
from our vocabulary unless we are talking about a place for potatoes anddigital
carrots.
Instead, we should discuss the "return path" when we talk about that node
in
all of our products with zero volts on it. Then when the "money savers"
and
"isolationists" come to signal and power integrity engineers and start
talking about splits we can ask: "What? You are going to cut my return
path? How is the return current going to get between my analog and
sections? Where is my PDN return current going to go? How muchinductance
is that going to add to my loop?"digital
Analog designers often make the argument that sensitive analog circuits
should be isolated from digital by cutting the return path between them.
But the analog sections almost always have to communicate with the
sections with signal lines. If we cut the on-die return path, possiblythe
package return path and heaven forbid the PCB return path, what are thosethis
analog-to-digital signal paths going to do? The A and D reference nodes
are
potentially 100's of mV apart and the noise varies with frequency. Is
what we want? If we are really going to cut the return path between ourcomprehend
analog and digital sections, then we should only use differential signals
for all A-to-D communication.
If we call it what it is - cutting the return path - we begin to
how much damage we are doing to ourselves with return-path splits."earth."
BTW, if we are talking about safety issues, we should use the word
and
Regards,
Larry
PS - These comments apply to signals higher than a few MHz. Sensitive
audio
signals where board traces are not long enough to be transmission lines
long audio cables are a different matter. In these cases, a startopology
makes sense.AC
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Martin Rowe
Sent: Tuesday, November 15, 2016 12:39 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Caps between "isolated grounds"?
The term "ground" is probably the most misunderstood and misused term in
electrical engineering. I blame the universities. They start their
electrical engineering instruction with DC circuits and then progress to
circuits with resistors, inductors, and capacitors. But the ideas ofdesigned
parasitic and nonschematic effects are seldom discussed in classes.
Usually,
lab assignments are relatively low-frequency projects -- probably
to ensure parasitic effects aren't encountered.ground
--Bruce Archambeault
http://www.planetanalog.com/author.asp?section_id204
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Lee Ritchey
Sent: Tuesday, November 15, 2016 3:24 PM
To: dbrooks9@xxxxxxxxxxxxxxx; dmarc-noreply@xxxxxxxxxxxxx;
si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Caps between "isolated grounds"?
Sometimes I am prompted to cite Bruce Archambeault from IBM on what
is.hope
Here is a quote from him.
"Ground is the place where one plants seeds in the spring time in the
that come summer one will get a bumper crop of tomatoes."the
The reason for Agnd and Dgnd on an IC is to isolate the analog side of
IC from the digital side for the purpose of isolating the two circuitsprovide
inside the package, not outside it. They should share the same ground
plane on the PCB. Having two different grounds on the PCB does not
any performance advantage to the IC.not
Outside the IC, efforts should be made to insure the analog source does
share paths with digital signals. We usually do this by using shieldedtrace
cables leading to the analog source.
Hope this clears up some of this confusion.
Lee Ritchey
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Doug Brooks
Sent: Tuesday, November 15, 2016 8:33 AM
To: dmarc-noreply@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Caps between "isolated grounds"?
Occasionally some people use a capacitor between different grounds in a
misguided attempt to provide to provide a signal return path under a
that crosses over the plane split for signal integrity purposes."grounds"
This, of course, is usually a bad idea. The purpose for separate
in the first place was to isolate noise. All the capacitor does is ensureI've
the noise has a path between the two grounds.
(Note to Jeff: Please send me a current email address off-line.)
Doug
Loyer, Jeff wrote:
I was looking at some designs and found different ground symbolsby capacitors. Can anyone explain why this might be done? Everything
connected
seen or heard says this is a bad thing (I would connect them directly),but
I want to be sure I'm not missing something. I think there are some A/D
devices which have specific guidelines for separating digital and analog
grounds, but I don't think they'd be connected by caps.
Thanks,
Jeff Loyer
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
--
********************************************
See Doug's latest book, available on Amazon.
"PCB Trace and Via Currents and temperatures; The Complete Analysis"
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at: //www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List forum is accessible at:
http://tech.groups.yahoo.com/group/si-list
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
