[time-nuts] UBlox GPSDO

Bob Camp kb8tq at n1k.org
Sun Apr 19 09:24:10 EDT 2015


On a practical basis - in a GPSDO you want to be able to “tune” the filter (like you
tune a control loop). That involves getting at the individual coefficients. Doing 
that is not what these chips are designed to allow. 

You can do the whole control loop with a < $1 MCU, so it’s not a big impact to 
your costs or your board area. 5x5 mm parts are pretty common. 


> On Apr 18, 2015, at 8:28 PM, Chris Caudle <chris at chriscaudle.org> wrote:
> On Fri, April 17, 2015 11:55 pm, Mark Sims wrote:
>> The SiLabs part only supports loop filter time constants down to 60Hz.
>> GPS loop filters usually use values in the 100's to 1000's of seconds.
> They have other parts with loop filters down to 4Hz, and I thought I saw a
> new part recently which could go down to 0.1Hz.  Definitely not 1000's of
> seconds though.
> -- 
> Chris Caudle
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