[time-nuts] GPS and PLL's...

Magnus Danielson magnus at rubidium.dyndns.org
Sun Dec 28 00:17:11 UTC 2008


Bales, Tracy skrev:
> I just started receiving the Time-Nuts emails...I admit that I've got a
> lot of learning ahead of me.
> 
> I've got a Trimble GPS module that outputs a 10 uSec wide pulse every
> second.  Now this is where I need some education...
> 
> How would you use the 1 PPS output to steer a phase locked loop running
> at 10MHZ?  Are you dividing the 10MHZ clock by 10 million?

That is usually what is done.

> If you are dividing by 10 million, wouldn't it take forever for the PLL
> to lock?

No, you get a fairly good idea about the initial frequency error in just 
the first seconds, using a PI-regulator is usually done. You can 
bootstrap it for a quicker lockup by raw-adjusting phase and possibly 
also frequency.

> See, I gave everyone warning about my learning curve!!!  Thanks...

Many of your fellow new friends here have been there, so no big worries.

If you look in the archives you will find this issue discussed over and 
over. You will also find links to several sites, include TvB. Do follow 
up on those links as there is usually lot of good info nearby.

Cheers,
Magnus




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