[time-nuts] Digital Phasae Lock Loops

Ole Petter Ronningen opronningen at gmail.com
Sat Oct 17 15:09:40 EDT 2015


Quartzlock makes a couple of interesting digital PLL-modules, marketed
specifically as ultra low noise cleanup loops. The datasheets contain a lot
of interesting and useful information about the software architecture - not
enough that *I* can recreate it, but perhaps someone more skilled than me
can.

Very interesting stuff:
http://quartzlock.com/product/timing-modules/digital-phase-lock-loop

Does anyone know of a reference where more information about this approach
can be found? I am impressed they can do all that in a PIC 16F689..

On Sat, Oct 17, 2015 at 4:48 PM, Jim Lux <jimlux at earthlink.net> wrote:

> On 10/17/15 6:17 AM, Alex Pummer wrote:
>
>>
>> actually, that is a ketch 22, if the loop bandwidth is to low, you will
>> have low noise , but it may will not lock at all, an other way to try to
>> filter out the noise, also you may make the loop filter digital, but
>> leave the the PLL analog, that could have  the possibility to have the
>> advantage to be able to change the loop bandwidth  increase for locking,
>> and reduce after the detected locking
>>
>
> changing  loop bandwidth between acquisition and tracking, or, similarly,
> (effective) loop bandwidth that changes with SNR are pretty common
> strategies.
>
> In the deep space transponder world (where you are acquiring and tracking
> a very narrow carrier at -155 or -160 dBm against noise of -170dBm/Hz) you
> also want to know what order filter you should be using in the tracking
> loop.  If there's an expectation that the frequency being tracked is
> changing (e.g. Doppler), then a low order loop may not be the best choice.
>
>
>
>
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