The Well Tempered Master Clock - Building a low phase noise/jitter crystal oscillator

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Hi all ...

Hmmm ... I would like to tread carefully here because this is not an area where I am that knowledgeable ... but comparing the phase noise of the SC-Cut at 22.58 MHz that was posted in #2017 with the phase noise of the AT cut at 11.29 MHz that Andrea posted in #5 - and considering that doubling an oscillator's frequency theoretically should give ~6 dB phase noise increase - then the SC-cut in #2017 is a couple dB worse at 1 Hz and 10 Hz and then the two oscillators are more or less equal when going up in frequency (the SC-cut could be a couple dB better at higher frequencies).

I do notice though that the RMS jitter value for the Driscoll cyan colored version (200uW drive level) is 8.9 fs whereas for the AT cut (Clapp) it is 0.4 ps - which is quite a difference.

Am I missing something - or do they measure more or less identical at lower frequencies (when considering the 6 dB phase noise increase per octave) ... ?

Cheers,

Jesper
 
Hi all ...

Hmmm ... I would like to tread carefully here because this is not an area where I am that knowledgeable ... but comparing the phase noise of the SC-Cut at 22.58 MHz that was posted in #2017 with the phase noise of the AT cut at 11.29 MHz that Andrea posted in #5 - and considering that doubling an oscillator's frequency theoretically should give ~6 dB phase noise increase - then the SC-cut in #2017 is a couple dB worse at 1 Hz and 10 Hz and then the two oscillators are more or less equal when going up in frequency (the SC-cut could be a couple dB better at higher frequencies).

I do notice though that the RMS jitter value for the Driscoll cyan colored version (200uW drive level) is 8.9 fs whereas for the AT cut (Clapp) it is 0.4 ps - which is quite a difference.

Am I missing something - or do they measure more or less identical at lower frequencies (when considering the 6 dB phase noise increase per octave) ... ?

Cheers,

Jesper

As I said the best phase noise performance is reached with SC-Cut overtone crystal around 5MHz (unloaded Q greater than 2M) and this has been demonstrated with the phase noise plots of both new oscillators using the 3rd overtone Laptech SC-Cut crystal at 5.6448MHz.
When the frequency of the crystal increases also the phase noise increases.

So I think the best solution is just to use an oscillator with a crystal at lower frequency (around 5MHz) followed by a frequency multiplier.

We are also working on a very low phase noise frequency multiplier.

Stay tuned!
 
Here you will find the original articles about the development of this low jitter oscillator:


Radio & Audio Artikelen


Bold articles are in English.

These articles are related to the first oscillator published in this thread, the Colpitts-Clapp using AT-Cut crystal.

The plots published in the last pages of the thread are related to a pair of totally different circuits using SC-Cut oscillators that have nothing to do with the Colpitts-Clapp: a differential circuit and a Driscoll type.
 
And now the phase noise plots of the new Driscoll oscillator, shielded and battery powered, with SC-Cut crystals at 5.6448 and 22.5792 MHz.
 

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Can you injection lock the 22MHz with the 5MHz? You may get a reduction in phase noise on the 22MHz. If you have both . . .

It could be a nice solution but adds complexity and overall becomes a little expensive, so the first option to get better results at 22MHz will be starting from the 5MHz crystal followed by a couple of low noise frequency doubler.
 
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