[time-nuts] Brooks Shera

Chris Albertson albertson.chris at gmail.com
Mon Mar 25 16:11:14 EDT 2013

On Mon, Mar 25, 2013 at 12:20 PM, Attila Kinali <attila at kinali.ch> wrote:

The PPS signal is not sent direct to the 74HC4520.  The PPS first
drives "Phase Detector 3" that is built into the 4046 chip.  this is
an RS flip flop.  Notice it is "RS3 OUT" that drives the 4520.    RS3
uses both the PPS signal and the divided down VCXO to create "RS3 OUT"
I think this gives a minimum pulse width, I'm not sure

> I dont know why this isnt a big issue with the Shera GPSDO.
> I guess that the specs of the 74HC4520 are very conservative
> an that the minimum clock pulse length is rather in the range
> of 5ns than 15ns for most devices and operation temperatures.
> It might also be that the probability of bits being affected
> is less for the upper bits than for the lower bits.
> Or the PI loop is stable enough to deal with the additional noise.
>                         Attila Kinali
> --
> The people on 4chan are like brilliant psychologists
> who also happen to be insane and gross.
>                 -- unknown
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.


Chris Albertson
Redondo Beach, California

More information about the time-nuts mailing list