[time-nuts] Low Phase Noise buffer

Magnus Danielson magnus at rubidium.dyndns.org
Fri Feb 19 09:23:11 UTC 2010


WarrenS wrote:
> 
> T&F Nut question
> 
> Is the high frequency phase noise of a buffer important when the 
> Oscillator is used just as the Reference for taking ADEV data?
> The current (2005) writings say that ADEV phase data should be bandpass 
> filtered which removes all the High freq edge jitter.
> If that is the case, Does a buffer's added HIGH FREQUENCY phase noise 
> and jitter have any effect on the ADEV numbers when using modern, high 
> resolution, mixer type, Time interval counters? Of course the low 
> frequency type of buffer noise would still be important.
> 
> Previously there was some confusion and disagreement on the subject. 
> What are the latest opinions?

The white noise which is the only dominant noise at higher frequencies 
goes down into the lower range and do contribute to the ADEV measures 
there, even if filtered. This filtering will affect lower-tau measures 
more than mid or high tau measures. Telecom standards prescribe 
filtering and tau0 for their reference measures for repeatable measures.

The filtering has been debated. The estimators will filter themselves 
regardless when m has become a number of multiples, essentially when the 
filter bandwidth becomes large compared to the inverse of the tau.

If the noise is benign white noise it should be kept at a low level, but 
work on flicker noise is where most effort should be spent.

Cheers,
Magnus



More information about the time-nuts mailing list