[time-nuts] Tight-PLL - YOU DON'T NEED TO READ IT IF YOUR FED-UP WITH THE THREAD SO HIT DELETE NOW!
Steve Rooke
sar10538 at gmail.com
Sat Jun 5 10:26:57 UTC 2010
On 5 June 2010 22:06, Steve Rooke <sar10538 at gmail.com> wrote:
> On 5 June 2010 19:07, Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
>> Wrong again.
>
> No, I'm not wrong Bruce.
>
>> 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.
>
> This process is exactly replicated by oversampling the EFC and
> determining the average for a fixed time period.
I guess I should add that this process is called Integration
estimating with finite sums but I thought you would have already known
that so just gave the abbreviated term.
> If you can't see that this performs exactly the same function, I don't
> know what will convince you.
>
> Steve
>
>> 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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>>>
>>
>>
>>
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>
>
>
> --
> Steve Rooke - ZL3TUV & G8KVD
> The only reason for time is so that everything doesn't happen at once.
> - Einstein
>
--
Steve Rooke - ZL3TUV & G8KVD
The only reason for time is so that everything doesn't happen at once.
- Einstein
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