Hi Vinod, It is no surprise that the simulation did not show anything. Did you model the system enclosure with all its cavity resonances as well as slots, seams, and all the cables as well? I think it is nearly impossible to simulate the complete system to predict radiation. I view simulations as a way to evaluate simple structures to understand how emissions occur and then use that knowledge in combination with factors that are not easy to simulate to estimate emissions. It takes so little energy extracted from a signal to cause an emissions problem it is quite possible to have great looking waveforms and still have an emissions problem. I do an experiment in one of my seminars where the waveform at the end of the structure looks really good, but the structure fails emissions by something like 40 dB! For instance, is the risetime of a clock just slightly slower than one would expect? Where did that high frequency energy go? Possibly into emissions due to a layout issue. Although some waveform anomalies definitely can cause EMC problems, a great looking waveform may still be a problem. ICs couple strongly to any nearby conductors which then radiate nicely where the IC would have been too small physically to be a problem on its own. Of course, board layout issues are another possibility. Knowing how the emissions get out into the wild can often help in tracking down the source. Measurements involving wire loops (fancy name = magnetic field probes), current probes, network analyzers or spectrum analyzers with directional couplers to measure resonances of physical structures, and so on. There are so many possibilities for your case, much more detail would be needed to avoid having you waste you time on a "wild goose chase." Of course another possibility is there is a common problem in the circuits you are working with that causes the emissions problem and is easy to avoid. Generally, one is really lucky if this is the case, but if it exists there are probably a number of people on this list that can help. Doug On 1/6/12 9:27 PM, vinod ah wrote: > 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 > > > -- ------------------------------------------------------- ___ _ Doug Smith \ / ) P.O. Box 1457 ========= Los Gatos, CA 95031-1457 _ / \ / \ _ TEL/FAX: 408-356-4186/358-3799 / /\ \ ] / /\ \ Mobile: 408-858-4528 | q-----( ) | o | Email: doug@xxxxxxxxxx \ _ / ] \ _ / Website: http://www.dsmith.org ------------------------------------------------------- ------------------------------------------------------------------ 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