The short answer is there should be only one ground in your PCB.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Boris Bakshan
Sent: Saturday, December 3, 2016 1:04 PM
To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
Cc: si-list@xxxxxxxxxxxxx; dmarc-noreply@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Caps between "isolated grounds"?
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 a"ground"
meter or scope when measuring a voltage.
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 a good design practice. Another possibility is that in theory, you
might 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 potatoesbetween them.
and 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 digital sections? Where is my PDN return current going to go?
How much inductance is that going to add to my loop?"
Analog designers often make the argument that sensitive analog
circuits should be isolated from digital by cutting the return path
But the analog sections almost always have to communicate with thesplits.
digital sections with signal lines. If we cut the on-die return path,
possibly the package return path and heaven forbid the PCB return
path, what are those 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 this what we want? If we are really
going to cut the return path between our 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
comprehend how much damage we are doing to ourselves with return-path
"earth."
BTW, if we are talking about safety issues, we should use the word
classes.
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 and long audio cables are a different matter. In
these cases, a star topology makes sense.
-----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 AC circuits with resistors, inductors, and capacitors. But the
ideas of parasitic and nonschematic effects are seldom discussed in
Usually,connected by caps.
lab assignments are relatively low-frequency projects -- probably
designed to ensure parasitic effects aren't encountered.
--Bruce Archambeault
http://www.planetanalog.com/author.asp?section_id=3204
-----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
ground is.
Here is a quote from him.
"Ground is the place where one plants seeds in the spring time in the
hope that come summer one will get a bumper crop of tomatoes."
The reason for Agnd and Dgnd on an IC is to isolate the analog side of
the IC from the digital side for the purpose of isolating the two circuits
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
provide any performance advantage to the IC.
Outside the IC, efforts should be made to insure the analog source
does not share paths with digital signals. We usually do this by
using shielded 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
trace that crosses over the plane split for signal integrity purposes.
This, of course, is usually a bad idea. The purpose for separate "grounds"
in the first place was to isolate noise. All the capacitor does is
ensure 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
I've 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
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
