[time-nuts] PLL question

[Magnus Danielson]

Ed Palmer wrote:
> Navsync doesn't really call it a synthesizer, they call it a Numerically 
> Controlled Oscillator (NCO).  My tests suggest that they're doing what 
> others have done on the 1 PPS output - change the state of the 10 MHz 
> output (high to low or vice versa) on a transition of their internal 120 
> MHz clock.  This means that you occasionally get a pulse that's ~8 ns 
> shorter or (presumably) longer than normal.  My unit puts out a short 
> pulse about 200 times per second.  Navsync has an app note where they 
> say that for some applications a phase-locked cleanup oscillator will be 
> required.

This 200 Hz tone (and overtones) needs to be suppressed. The size of it 
is 8/100 = 80 mUI. A 10 Hz BW with PI regulation would suppress this 
with about 3 + 6 + 20 = 29 dB. This brings it from 8 ns to 280 ps.
I assume a -6 dB/Oct slope as it forms a 2'nd degree loop.

Cheers,
Magnus