[time-nuts] More on SiLabs 5340

John Miles john at miles.io
Tue Jan 30 22:27:55 EST 2018

> -----Original Message-----
> There is a small detail that puzzles me: the ADEV for the internal
> reference 10MHz and 30MHz bends upwards at tau greater than 0.1s.
> Shouldn't that be visible by a change in slope in the phase noise
> plot at ~10Hz as well?
> 			Attila Kinali

Linear drift (which is what's happening here) has a bigger effect on the overall gestalt of an ADEV plot than it will on a phase noise plot.  This is because long-term drift looks similar to DC offset or noise at extremely low frequencies, both of which are attenuated by an HPF stage prior to each FFT segment.  But ADEV doesn't benefit from DC removal, and since it doesn't converge in the presence of drift, you get the usual upturn in the trace at increasing taus. 

When you see a highly-elevated noise trace at low offset frequencies, it's also a good idea to check for glitches in the 'f' measurement view, although in this case the L(f) spectrum is very typical of these sorts of parts. 

-- john, KE5FX
Miles Design LLC

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