[time-nuts] A philosophy of science view on the tight pll discussion

jimlux jimlux at earthlink.net
Sat Jun 5 13:07:55 UTC 2010

Magnus Danielson wrote:

> Also, modern cheap programmable TCXOs break the model as they have a 
> hump in the phase noise due to their locked PLL, which the original 
> model does not allow for. The autocorrelation function will be quite 
> different. Notice how this ripples over to other locked oscillators such 
> as passive masers, GPSDO etc.

Yes.. once one moves beyond a simple oscillator/resonator and amplifier, 
you're out of the zone where the simple Leeson model will work all the 
time.  the curves have lumps and bumps, and simple approximations of 
integration don't work any more.

And then, you have the whole explaining "why do I care what the phase 
noise/Allan deviation is" or trying to relate noise performance to 
overall system performance.  (e.g. what happens if the phase noise at 
1MHz offset is 20 dB worse than expected?)

For some simple cases, blackboard sketches of reciprocal mixing and such 
help, but when it gets more complex... or when you're trying to relate 
an integrated phase jitter spec to the distribution that creates it....

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