Hi Bala, On the line side of the isolation transformer on a PCB you do not need a reference plane for Ethernet differential signals. Otherwise, noise on the planes could couple to the differential pair and could cause radiated emissions. Since Ethernet cables are generally unshielded and are typically very long they act as very good antennas. So, removing the reference planes (all planes) on the PCB on the line side of the transformer is a good idea. Since reference plane is needed on the chip side of the transformer for the terminations and ESD capacitors the planes are usually removed at the mid point of the transformer package. Thanks, Ram Chundru Kbalasubramanian@xxxxxxxxxxxxxx wrote: Dear Experts, EMI radiated emission is failing in our current ethernet product design .All the ethernet harmonics are appearing in the emission list. I am told that removing the reference plane below the ethernet differential pair signals (RX & TX) will solve this issue. For differential signals reference plane is not required since the return current flows through the other conductor. But will the presence of reference plane have negative effect? Sincerely K.Balasubramanian Project Leader - Hardware. ------------------------------------------------------------------ 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 or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu Ram Chundru System Level ESD Engineer Texas Instruments Inc. 12500 TI Blvd, MS 8734 Dallas, TX 75243 Phone: 214-480-1654 www.emc-engineer.com --------------------------------- It's here! Your new message! Get new email alerts with the free Yahoo! Toolbar. ------------------------------------------------------------------ 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 or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu