[time-nuts] Tight-PLL - YOU DON'T NEED TO READ IT IF YOUR FED-UP WITH THE THREAD SO HIT DELETE NOW!

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Jun 5 03:07:57 EDT 2010


Wrong again.

The integration/averaging referred to occurs when one counts the output 
transitions of the VFC for a fixed time interval.
This process needs to be replicated using the sampled EFC data if one is 
to measure ADEV.

Bruce

Steve Rooke wrote:
> I think I have found the source of the "integration" issue. I've spent
> some considerable time ploughing through as many sources of
> descriptions on ADEV, AVAR and the tight-PLL method. I've even tried
> looking for the infamous "finite time interval integrator" which seems
> to be highly notable by it's complete absence on Google. Well,
> eventually the answer struck me directly in the eye, the source of the
> integrate issue comes directly down to the original paper that Warren
> posted a link for:-
>
> D. Tight phase lock loop method
>
> The second type of phase lock loop method (shown in figure 1.7) is
> essentially the same as the first in figure 1.6 except that in this
> case the loop is in a tight phase lock condition; i.e., the response
> time of the loop is much shorter than the sample times of
> interest--typically a few milliseconds. In such a case, the phase
> fluctuations are being integrated so that the voltage output is
> proportional to the frequency fluctuations between the two oscillators
> and is no longer proportional to the phase fluctuations (for sample
> times longer than the response time of the loop). A bias box is used
> to adjust the voltage on the varicap to a tuning point that is fairly
> linear and of a reasonable value. The voltage fluctuations prior to
> the bias box (biased slightly away from zero) may be fed to a voltage
> to frequency converter which in turn is fed to a frequency counter
> where one may read out the frequency fluctuations with great
> amplification of the instabilities between this pair of oscillators.
> The frequency counter data are logged with a data logging device. The
> coefficient of the varicap and the coefficient of the voltage to
> frequency converter are used to determine the fractional frequency
> fluctuations, yi, between the oscillators, where i denotes the ith
> measurement as shown in figure 1.7. It is not difficult to achieve a
> sensitivity of a part in 1014 per Hz resolution of the frequency
> counter, so one has excellent precision capabilities with this system.
>
> http://tf.nist.gov/phase/Properties/one.htm
>
> The relevant section here is "the response time of the loop is much
> shorter than the sample times of interest--typically a few
> milliseconds. In such a case, the phase fluctuations are being
> integrated so that the voltage output is proportional to the frequency
> fluctuations". So what this says is that by incorporating a PLL-loop
> filter that has a B/W much wider than the sample time, the phase
> fluctuations are integrated into the reference oscillator such that
> the control voltage of the tight-PLL now reads frequency which is
> unlike the loose-PLL which directly records the phase relationship
> between the oscillators. So the term "integrated" here is used a verb
> and not a noun, therefore it is an intrinsic function of the design
> not a separate process.
>
> Steve
> --
> Steve Rooke - ZL3TUV&  G8KVD
> The only reason for time is so that everything doesn't happen at once.
> - Einstein
>
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