[time-nuts] GPSDO control loops and correcting quantizationerror

[Dennis Ferguson]

On 16 Sep, 2012, at 16:30 , Poul-Henning Kamp wrote:

> In message <34D5C3CE-6B3D-4944-996A-7637373B2857 at gmail.com>, Dennis Ferguson wr
> ites:
> 
>> I'm not sure there could be a difference between the goals of
>> frequency accuracy and time accuracy that would effect that time
>> constant.

Note that the "that time constant" referred to here, the topic of
the message I was responding to, was explicitly a PLL time constant.
If you have decided to use a PLL as your control discipline I think
you end up with the same time constant whether your goal is accurate
frequency or accurate time since, with a PLL, these end up being
the same problem.

> It does. 
> 
> A PLL more or less corresponds to an "PI" regulation, where a FLL
> only needs to have the "I" term.
> 
> Because you don't have the interaction between the P and I terms,
> the I-timeconstant can be longer.

This sounds right.  As I said, if you pick a control discipline other
than a PLL, as might be advantageous to do if your concern is solely
with accurate frequency, then the optimum might be different.  If you
are using a PLL in both cases, however, then the problems are
essentially the same.

Dennis Ferguson