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 -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
