Vinod, Many possibilities come to mind, but since the failing frequency is at the clock frequency, my first question would be: how are the clock lines terminated? I would also be looking at the routing - do the clocks cross any plane breaks? Do the clocks change layers? Do the transition vias have accompanying ground return vias? You need to follow not just the routing, but also the associated return currents to look for inductive loops. Alan Hilton-Nickel Oracle Corp Sent from my Verizon Wireless 4G LTE Phone -----Original message----- From: vinod ah <ah.vinod@xxxxxxxxx> To: SI-LIST <si-list@xxxxxxxxxxxxx> Sent: Fri, Jan 6, 2012 21:27:34 PST Subject: [SI-LIST] DDR3 clock failing radiation Tests Hi all, I am facing problems related to EMI. I am having a ASIC with 2 DDR3 controllers running at 513MHz clock. I am interfacing 2 memories to each of the controller. So totally 4 memory chips on board, all running at 513MHz clock. During pre-compliance radiation testing in FCC certified lab, we observed 513MHz in the spectrum with 15dB above the CISPR class B limits i.e. test failing by 15dB !!!!! I tried to corelate this result with Hyperlynx spectrum analyzer simulation and SI simulation. The waveforms and radiation level looks fine in Hyperlynx i.e. no issues seen. Initially i had suspected the layout, but hyperlynx SI simulation looks fine and also the clock & dqs waveforms in CRO looks fine i.e. no ringing/overshoot etc. The DDR3 clock is routed in inner layer 3 of six layer stack up of the board. I have tried using EMI shield, but still i am failing by 8dB. Only thing i have not yet tried is spread spectrum clocking. But I am unable to find the source of problem. Can you please help me out in finding the sourceto this problem. I understand that it is very tuff to provide solution to this problem without seeing the layout, but i am expecting some tips so that i can move ahead in debugging the problem. Regards Vinod A H ------------------------------------------------------------------ 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 ------------------------------------------------------------------ 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