[time-nuts] Driving clocks from 1pps

[Chuck Harris]

Tom Van Baak wrote:
>> 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.

No Tom, you misunderstand.  The 50% duty cycle pulse provides the
rising and falling edges.  The small capacitor differentiates
that to produce a positive going, or a negative going pulse to
make the motor move.

-Chuck Harris