[time-nuts] Can (will) a M12+T generate a negative sawtooth message ?

Tom Van Baak (lab) tvb at leapsecond.com
Sun May 18 19:51:56 EDT 2014


Hal,

Yes, there are negative delays. The goal is that the physical 1PPS output is, on average, exactly on-time. If designed right, that means as many negative offset pulses occur as positive offset pulses. The spread gives you the RMS value. 

This is exactly what you want for a GPS timing receiver.

/tvb (i5s)

> On May 18, 2014, at 1:42 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
> 
> The ref output is the minimal delay through the chip covering the input and 
> output pad buffers.  It will vary slightly with temperature and voltage.
> 
> There are no negative delays in that sort of chip.  It's just a bunch of 
> gates/buffers with a carefully calibrated delay.  (For a negative delay, you 
> would need something like a PLL.)
> 
> If the delay from the M12+T might be negative, set the antenna cable delay to 
> be a bit short and add on a constant in software.



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