Jeff wrote on 8/6/2017 6:38 AM:

You are making pointless distinctions. A phase locked loop is not defined
by its mechanics but by the nature of its control. The Shortt clock
maintains the relative *phase* of the two clocks by brief adjustments to
the frequency via a spring. This is controlled by measuring the relative
*phase* of the two clocks.


Wrong! It does NOT measure the relative phase, it makes NO measurement of
the phase difference. All it does is detect if there is a phase lag of any
degree. It could be a fraction of a degree or 180 degrees, the same
correction is then applied regardless.

....and that is a measurement. It determines if the relative phase is plus
or minus, a binary measurement. This is exactly the same as the measurement
taken by a 1 bit ADC. Even though it is one bit it is still a measurement.


It's that simple. You are just making things more complicated by talking
about the details of how the adjustment works and the time function of the
frequency. NO PLL can keep the two clocks perfectly in sync.

Calling it open loop is just absurd. The loop is closed because it
*measures* the phase of the clocks and adjusts the phase according to the
measurement. It may be binary, but the adjustment is controlled by the
measurement.

Wrong again it is open loop, there is no measurement, just the same
adjustment regardless of the phase difference.

Totally wrong. The phase adjustment varies from a constant about to ZERO!
Again it is a binary adjustment.

If there was a three level range of measurement and adjustment +, 0, -,
would that be enough to constitute a measurement and adjustment so it
becomes a PLL? If not, how many bits are required? If any number of bits
can't do it are digital PLLs not PLLs?

--

Rick C