[time-nuts] an interesting problem

Magnus Danielson magnus at rubidium.dyndns.org
Sat Feb 5 16:57:07 UTC 2011


On 05/02/11 17:30, jimlux wrote:
> On 2/5/11 8:11 AM, Magnus Danielson wrote:
>> What you can do is you generate your tick clock at any division greater
>> than 7*14 (if I understood the timing correctly). Say you divide your
>> clock with 200 (about 3 us period if I got it right). Then you would get
>> about half the period between your ticks would have random delay and the
>> rest is silent.
>
> yes, I'll probably use a divisor of 66 million to get 1pps ticks.

OK, so you got 66 MHz clock... I'd use a 66000 divisor to get 1 kHz.
The period of the 0-14 noise would be 106,060606 ns but the round-off 
error of that can be limited since it is only a phase-modulation so 
worst-case would be 14 times.

>> You then make TI measurements against some suitable clock. From that you
>> should then be able to rebuild your baseline time difference, detect the
>> random delay of 7x[0-14] and once you done that re-stamp those with the
>> suitable time and you now have a new time-series which all seems to be
>> experiencing the random delay of 0. From then on just do the ADEV or
>> whatever you want to do according to standard processing.
>
>
> That's sort of what I was thinking.. all dependent on whether the
> variance is small enough to determine the N

Making the period of your ticks short enough should make the noise less 
of a concern.

Cheers,
Magnus

>>> or, is a real oscillator going to have an instantaneous variance that is
>>> comparable to or greater than 1 clock pulse?
>>
>> No, probably not unless you got a seriously bad design, which you would
>> probably know by now anyway. For short time-spans, deterministic noise
>> (such as your random buffer delay) and white noise will dominate.
>
> To the lab.. (well, on Monday..)
>
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