[time-nuts] typical phase nosie and ADEV plot of an OCXO

Magnus Danielson magnus at rubidium.dyndns.org
Wed Mar 14 13:47:15 UTC 2012


On 03/14/2012 11:22 AM, Attila Kinali wrote:
> Hi,
>
> I'm currently writing a short article on crystal oscillators and am
> looking for plots of "typical" phase noise and ADEV of an OCXO.
> But unfortunately, i couldnt find any, so far. Only discrete numbers
> from the data sheets, or phase noise plots only from scientific papers.
>
> Does anyone have something like this at hand?

I know I should add one to the Wikipedia Allan Deviation article. Let me 
know if there is anything other which is missing in that article so I 
can add to it.

What you should have is essentially a bath-tub curve with a 1/tau slope 
for the white phase modulation (WPM) noise, a roughly 1/sqrt(tau) slope 
from the flicker phase modulation (FPM) or white frequency modulation 
(WFM) and then a flat part due to the flicker frequency modulation 
(FFM). See the table in [1].

At higher tau the systematic effect of frequency drift comes in, and if 
included into the Allan Deviation it rises with tau [2]. As a systematic 
effect, it should not really be included into the ADEV plot, but you 
usually see it in practical measurements.

[1] http://en.wikipedia.org/wiki/Allan_variance#Power-law_noise
[2] http://en.wikipedia.org/wiki/Allan_variance#Linear_response

The existence of WFM and FFM noises is due to the Leeson model.

Cheers,
Magnus




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