Hi Since ADEV is a measurement of noise, you want to be very careful about just which noise you keep and which noise you "throw away".
Bob On Jun 19, 2010, at 7:06 AM, Magnus Danielson wrote: > On 06/19/2010 12:49 AM, WarrenS wrote: >> Say you have a nice logic gate with 1 ns delay >> If you make it all nice and clean, and repeatable such as constant PS, >> rise time etc. >> Then one can get repeatable results say 100 times better from cycle to >> cycle in the short term. >> so down to 10ps repeatable. >> Now make things even more clean with no variations and assuming random >> noise. >> Now if one is doing this at 10 MHz and only cares about the average over >> 0.1 sec (10 Hz) >> One can average 1,000,000 readings of the 10 ps jitter >> If they are truly random, that can give you a 1e-3 improvement (square >> root of number of samples averaged) >> so now down to 10 fs of average jitter at 10 Hz for a 10 MHZ gate >> starting with a 1ns initial delay. > > The square root improvement assumes white noise, and will work when white > noise dominates. A logical gate or any other amplifier will also have flicker > noise, which doesn't average out like that. The meaningful length of > averaging thus depends on the cut-off frequency between white and flicker > noise. To analyse it, Allan variance and friends needs to be applied. Thus, > only for short-term stability may straight averaging work for estimation. > > Cheers, > Magnus > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
