[time-nuts] TPLL secret reveled

[John Miles]

> Warren, can you please clarify. From what I can see it actually
> uses a Minicircuits phase detector, right? That suggests what is
> being observed is a phase difference between the DUT and the
> REF, not a frequency difference.
>
> That analog phase measurement is then filtered and amplified
> into a pre-calibrated EFC correction to the REF which over a
> short time reduces the phase difference as seen by the phase
> detector. The digital stream comes from an ADC is connected
> to the EFC.
>
> So what does it mean to say "TPLL uses Freq not phase"? It
> looks to me like it uses both.

The VCO tuning voltage is proportional to frequency, as the VCO acts as an
integrator in a type-2 PLL like this one.  (Remember that the phase detector
is on the other side of the VCO.)

-- john, KE5FX