Hi: I’ll try to make this simple. At the frequencies of concern the traces are also antennas or transmission lines. You’d like to keep them as close to transmission lines as possible to reduce the radiation effects. Unfortunately the close coupling and lack of complete symmetry and other discontinuities makes the traces more like antennas. The effect is minimized if the enclosed loop is kept small and the traces are kept short.
Fred Townsend DC to Light From: [email protected] [mailto:[email protected]] On Behalf Of [email protected] Sent: Thursday, October 28, 2010 12:38 AM To: [email protected] Subject: Gigabit ethernet placing and routing related question Hi, I am currently working on a project involving routing of gigabit ethernet signals between a PHY and the outside world. Basically, after going through the routing recommendations, it is most of the time recommended to have the PHY close to the magnetics close to the RJ45 connector. The closer the better. I went though the si-list about this subject and I found some advice like the transformer should be close to the phy but the CM choke should be close to the connector. The idea of having an EMI protection device close to the connector seems to make sense but I do not understand the reason why the transformer should be close to the PHY : what is the advantage versus having both the magnetics and the CM choke near the connector and therefore a "long" distance between the PHY and the magnetics ? Although having the CM choke near the connector seems to make sense I have also read about the fact that it it was ok to have quite a distance between the transformer/choke and the connector but no mention there about some restrictions concerning the PHY to transformer distance. Could someone, give (again ?) some insights into the pros and cons of each topology ? Best regards, JF Hasson - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher <[email protected]> David Heald <[email protected]>
