[time-nuts] Why are 1PPS signals so skinny?

Mike S mikes at flatsurface.com
Tue May 15 20:51:13 UTC 2012


On 5/15/2012 4:19 PM, Attila Kinali wrote:
> If the
> PPS pulse is short, it contains very little energy, which means
> the energy can be supplied by the small capacitors at the output
> driver. The longer the pulse gets, the more energy it needs.

The pulse is meaningless. It's only the leading edge that matters. I 
understand how shorter pulses may make for marginally cheaper electronics.

> Which might have a negative effect on their performance.

I might win the lotto. The question is exactly _how_ does it effect 
their performance, especially if they're synchronizing to the PPS signal.

> it's no use of having a fast
> rising edge, if the pulse colapses a couple ns later.

Huh? If ns is too short, and ms is too long, what makes us just right? 
And why are there so many timing receivers that only output on the order 
of 20 us, when there are so many inputs which may require a few ms?

PPS is edge triggered, not level triggered. Once the leading edge is 
transmitted (and it by necessity has a very fast rise time, so it looks 
to capacitors, transformers, etc. as a high frequency signal), the shape 
of the pulse really doesn't matter much. Some devices need more than a 
minimum above some threshold, but what ones need less than a maximum? If 
it doesn't look like a flat topped pulse, so what? As long as the decay 
is basically monotonic, and the receiver has some hysteresis (reasonable 
assumptions), it makes no difference.



More information about the time-nuts mailing list