Some points you may not see in app notes or datasheets: 1 - the app notes are very often wrong in their statements about length matching. They totally ignore the pin offset on the Phy, and the fact that it's self-correcting inside the package. 2 - the same for the wiring offset inside the connector. Get an RJ45 connector, break it open, and you will see what I mean - some wire/trace lengths are much greater than others, but the pin offset compensates for this. (I've convinced half our engineers about this - now the other half!) I've attached a photo of one to show you what I mean. Upon saying that, EACH CONNECTOR IS DIFFERENT! 3 - likewise for length matching between pairs - ie diff-pair1 and diff-pair2, both on the same port.. Some people tend to forget the huge descrepancies in the cable after it leaves the port. 4 - be aware that two 50ohm lines run closely coupled will not equal 100ohms differential. Because of coupling, each line will need to be 52-55ohm or so. Have fun. Richard >>> andrew@xxxxxxxxxxx 13/05/2005 8:14:15 a.m. >>> A quick Google of 'routing gigabit Ethernet pcb' yielded many results. One of which is: www.ee.duke.edu/~mbrooke/EE164.02/ Click> Spring_2004. There seems to be a lot of material that will help you out. There are definitely many more places where you can find these kind of resources. Best of luck, Andrew Noonan Sr. PCB Designer Topspin Communications (w)650-316-3398 (c)650-814-3677 -----Original Message----- From: icu-pcb-forum-bounce@xxxxxxxxxxxxx [mailto:icu-pcb-forum-bounce@xxxxxxxxxxxxx] On Behalf Of Kevin McCowan Sent: Thursday, May 12, 2005 12:53 PM To: icu-pcb-forum@xxxxxxxxxxxxx Subject: [PCB_FORUM] Re: Gigabit Ethernet circuit design I have done these before and I think standard practices for the type of nets (diff pairs) should take care of it. If you need more help check with the manufacturers of the chips and see if they recommend something. They are only 4 250 meg pairs. I have just made sure the nets aren't too long and keep other stuff a little away. I have done 3 or 4 of these and had no issues. Kevin McCowan Sr. PCB Designer TSI Telsys moose wrote: > Hi, > I need to read some information about how to layout > a pcb for Cigabit Ethernet Circuit Design. > and Layer 4 and Layer 7 forwarding machines. > is there any book that I can find some tips about these. > thanks ----------------------------------------------------------- To subscribe/unsubscribe: Send a message to icu-pcb-forum-request@xxxxxxxxxxxxx with a subject of subscribe or unsubscribe To view the archives of this list please login at //www.freelists.org. Our list name is icu-pcb-forum or go to //www.freelists.org/archives/icu-pcb-forum/ Problems or Questions: Send an email to icu-pcb-forum-admins@xxxxxxxxxxxxx Want to post a job listing ? DON'T DO IT HERE! Better yet, join our jobs listing forum. SUBSCRIBE: icu-jobs-forum-subscribe@xxxxxxxxxx POST: icu-jobs-forum@xxxxxxxxxx ----------------------------------------------------------- ----------------------------------------------------------- To subscribe/unsubscribe: Send a message to icu-pcb-forum-request@xxxxxxxxxxxxx with a subject of subscribe or unsubscribe To view the archives of this list please login at //www.freelists.org. Our list name is icu-pcb-forum or go to //www.freelists.org/archives/icu-pcb-forum/ Problems or Questions: Send an email to icu-pcb-forum-admins@xxxxxxxxxxxxx Want to post a job listing ? DON'T DO IT HERE! Better yet, join our jobs listing forum. SUBSCRIBE: icu-jobs-forum-subscribe@xxxxxxxxxx POST: icu-jobs-forum@xxxxxxxxxx ----------------------------------------------------------- NOTICE: This message contains privileged and confidential information intended only for the use of the addressee named above. If you are not the intended recipient of this message you are hereby notified that you must not disseminate, copy or take any action in reliance on it. If you have received this message in error please notify Allied Telesyn Research Ltd immediately. Any views expressed in this message are those of the individual sender, except where the sender has the authority to issue and specifically states them to be the views of Allied Telesyn Research.
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