[time-nuts] Notes on tight-PLL performance versus TSC 5120A
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Thu Jun 3 20:32:22 UTC 2010
If I may be allowed to summarize, it appears that Warren and Bruce
agree that integration is necessary to produce true ADEV
results. Warren asserts that the low-pass filtering his method uses
is "close enough" to integration to provide a useful approximation to
ADEV, while Bruce disagrees. So, the remaining points of contention
seem to be:
1. How close can a LPF implementation come to integration in ADEV
calculations, and
2. How close to true ADEV is "good enough"?
I humbly submit that trading insults has become too dreary for words,
and that neither Warren nor Bruce will ever convince the other on the
latter point.
I thus humbly suggest (nay, plead) that the discussion be re-focused
on the two points above in a "just the facts, ma'am" manner. One can
certainly characterize mathematically the differences between
integration and LP filtering, and predict the differential effect of
various LPF implementations given various statistical noise
distributions. If one is willing to agree that certain models of
noise distributions characterize reasonably accurately the
performance of the oscillators that interest us, one can calculate
the expected magnitudes of the departures from true ADEV exhibited by
the LPF method. Each person can then conclude for him- or herself
whether this is "good enough" for his or her purposes. Indeed,
careful analysis of this sort should assist in minimizing the
departures by suggesting optimal LPF implementations.
Best regards,
Charles
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