> We are encounter some EMI problem on 6x PCI 33 MHz clocks. If I > stagger these six clocks by 0.2 ns seconds away (assume the time > margin still meets) will it help EMI ? I think in principle it might, but maybe not. In the time domain the offset would need to be significant with respect to the clock signal's risetime. By doing so, the edges would be skewed from one another and wouldn't all coincide, which would reduce the peak current in the return path too. In the frequency domain, you should consider what frequencies are failing. This 0.2 ns corresponds to some phase shift at each harmonic frequency, and at high enough harmonics (in the vicinity of the 75th harmonic), the phase shift could give you some cancellation and EMI reduction. To get reduction of the 7th harmonic, the skew would need to be 2.1 ns. But part of the trick would be to make the skew predictable, to keep it consistent. What if one clock fanout part happened to have its outputs skewed 0.2 ns in the opposite direction? Plus, variations in loading on the clock pin from different PCI cards, would affect the results too. Regards, Andy ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org 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