Boris,
I have done essentially the same thing Lee has described in all of the
backplanes I have designed in the past, except that in our case the outer
PCB layers on both sides were "GND" plane, and the PCB was edge plated. This
created a faraday shield for all the internal layers. The backplane was
metalically connected to the shelf framework with screws without isolation.
There was only one "GND" in the system, including the line cards that
plugged into the shelves.
This "grounding" scheme was compatible with single-point ground/integrated
bonding network (SPG/IBN) and mesh/common bonding network(Mesh/CBN). Our
systems had to meet GR-1089-CORE - Electromagnetic compatibility and
electrical safety for network telecommunications equipment.
-48V Battery and Battery return powering the system was isolated from the
"Chassis GND" with an option to join the battery return to "chassis ground"
at the single power entry point.
Regards,
Bert Simonovich
Signal/Power Integrity Practitioner | Backplane Specialist | Founder
LAMSIM Enterprises Inc.
Web Site: http://lamsimenterprises.com
Blog: http://blog.lamsimenterprises.com/ ;
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Boris Bakshan
Sent: 7-Jan-17 1:16 PM
To: Lee Ritchey
Cc: si-list
Subject: [SI-LIST] Re: An Article on what ground is
Hi Lee,
Thank you for prompt reply.
So, in fact, you are making a direct connection between the logic ground of
the cards and the metalic chassis enclosure so that backplane ground (return
path of signals) , cards logic ground and metalic chassis enclosure are all
connected, did I get it right?
On Jan 7, 2017 7:57 PM, "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx> wrote:
Thanks for the nice feedback.
Aha! You have asked an EMI question! I use the ground plane in a
backplane as one side of my Faraday cage. Where that backplane meets
the flanges on the card cage, I leave the copper on the top layer and
connect that with vias to the ground plane in the backplane. Now,
there is the one connection between logic ground and the Faraday cage.
There can be no other connections such as on face places if one is to
avoid "leaking" at the cracks which is a common complaint when more
than one connection is made between logic ground and the Faraday cage.
Notice, I did not use the phrase "chassis ground" in this discussion.
I have used this method in dozens of systems with very good EMI results.
Hope this helps.
Lee
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]
On
Behalf Of Boris Bakshan
Sent: Saturday, January 7, 2017 5:24 AM
To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
Cc: si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: An Article on what ground is
Hi Lee,
Very good, comprehensive article, thank you.
What is your recommendation when it comes to backplanes? a backplane
is attached to the chassis with bolts/other conductive mechanical
parts. Do you recommend plating these PCB holes in the backplane? If
you do, should these holes be connected to (any) electrical net?
Thanks Lee.
On Fri, Jan 6, 2017 at 10:43 PM, Lee Ritchey
<leeritchey@xxxxxxxxxxxxx>
wrote:
I have written an article on ground following the brisk exchange on
this subject last month. I hope it clears up some of the confusion
around this subject.
Here is where it is on the web.
http://ubm.io/2ikEDat
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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