[SI-LIST] Re: Emission Problem with Ethernet
- From: steve weir <weirsi@xxxxxxxxxx>
- To: deepak Engineer <deepaksiengg@xxxxxxxxx>
- Date: Sat, 18 Sep 2010 13:44:05 -0700
Keep in mind that:
* Hundreds of millions of Ethernet ports have shipped using off the
shelf components that meet emissions requirements.
* The primary offender in EMC problems is common mode noise.
The most common EMC mistakes that people make are in:
* Component placement
* PCB stack-up
* Case bonding
* Routing
So check:
What are your common mode leakage paths?
--- Are you coupling your noisy circuit common to the Ethernet signals,
balanced or unbalanced such that it gets across your magnetics,
particularly your CM magnetics?
--- Did you put your ESD protection on the wrong side of the isolation
magnetics?
--- Did you route your ESD protection in such a way that you are getting
a lot of mode conversion?
--- Are you using a shielded enclosure?
------ If so, how does your noisy circuit common couple to that
enclosure? By accident, or specific design?
------ If not, how noisy is a simple wire antenna soldered to your
circuit common compared to your Ethernet cable?
Are your CM chokes any good?
---Are the magnetics you purchased from a reputable manufacturer? What
does the noise look like w/o the CM magnetics?
---Are they counterfeit?
---Are they gray market?
---Are they returns perhaps?
Additional CM choke(s) should not have killed your signal unless you
purchased chokes with entirely inappropriate characteristics. It sounds
like you connected them incorrectly. Even so, that may be moot, because
with a good layout, proper stack-up, and case bonding scheme the CM
choke in the RJ45 should have been good enough.
If you feel lost, pay an EMC consultant to review your design.
Steve.
deepak Engineer wrote:
> Hello Experts,
> I am working on improvement of Ethernet port.
> In design, we are getting a high emission at 125MHz of 53 dbuV(case:Ethernet
> communication via unshielded LAN-cable).
>
> I would like to reduce this db level below 40db.
>
> Circuit description:
> 1.RJ45 connector with inbuilt magnetic(with CM coil)
> 2.ESD protection on all four signals.
> 3.RJ45 connector is place on the corner of the PCB in cavity of C shape. i.e
> connector in not place on top of PCB, but solder in C shape cavity.
> 4. to reduce the emission, an external CM choke is used. which is not
> passing the signals(becasuse of Differential Signal level= 0.4Vp-p). so I
> shorted the footprint with links.
> 5. On RJ45, system is only using signal ground(no chassis ground).
>
> Restriction of the design:
> 1. can not use the chasis ground, due to placement problems.
> 2. can use only unshielded cable
>
> Could you please suggest some other possible way to handle this situation.
>
> I'm stressing on Chassis ground..
>
> Thanks,
> Deepak
>
>
> ------------------------------------------------------------------
> 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 technical documents are available at:
> http://www.si-list.net
>
> 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
>
>
>
>
--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
------------------------------------------------------------------
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 technical documents are available at:
http://www.si-list.net
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
Other related posts:
