[time-nuts] Software Sawtooth correction prerequisites?

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat May 19 18:30:49 EDT 2007


Angus wrote:
>
> The acam TDC-GP1 (~250ps res) and TDC-GP2 (~50ps res) were around 23
> and 15 euro respectively when I checked with them last year.
>
> I had been planning of trying a GP1, but have not done much on it
> recently. It seemed like it should be fairly straightforward to do a
> small module to accept the two pulses and spit out the results to a PC
> - much cheaper than a counter, even if generally less flexible.
>
> Some sort of hardware correction is also quite useful for feeding a
> good 1pps to other equipment that may not remove the sawtooth
> themselves, and allows easy checking of any effects of the sawtooth on
> them.
>
> Angus.
>   
Angus

This indicates that the cost of using say an Acam TDC-GP2 as a phase 
detector is comparable to using a Dallas programmable delay line to 
correct the sawtooth error.
Combining the 2 would allow the TDC-GP2 to be used to calibrate the 
delay of the programmable delay line (The TDC-GP2 has a built in 
autocalibration function).

Hardware correction is certainly necessary for legacy equipment and 
other equipment that cannot correct for sawtooth error.
In this case the hardware correction should be as accurate as possible 
and for some purposes the absolute delay of the PPS signal needs to be 
known.

Bruce



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