[time-nuts] Driving clocks from 1pps

Tom Van Baak tvb at LeapSecond.com
Thu Sep 4 23:36:38 UTC 2008


> I am in the middle of the design of a micro which uses a 10MHz crystal
> to provide a digital clock, but the time is kept in line via GPS using a
> 1pps NCO, which is steered digitally, rather than altering the 10MHz
> oscillator in GPSDO fashion.
> 
> The plan was to provide two outputs (biphase) at 1pps to drive slave
> clocks, but in the light of the notes from Brooke and Chuck, I would be
> better off just providing a single output, and use a series cacacitor.
> 
> Chuck, I would expect that the 1pps would need to be about 50% duty
> cycle, or at least have a pulse width of 100ms or so. I can imagine a
> clock driven from 1pps with a low duty cycle would sound quite
> different.
> 
> 73,
> Murray ZL1BPU

50% duty cycle is way overkill, perhaps even harmful. In the
'scope traces below you can see the IC generates just 50 ms
biphase pulses every second. That's 1/20, or 5% duty cycle.

http://www.leapsecond.com/pages/32kHz/

/tvb





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