[time-nuts] Digital PLL ICs, alternatives and digital loop filters

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Dec 16 17:26:30 EST 2006


Stephan Sandenbergh wrote:
> Hi,
>
>  
>
> Another question for today - I have checked out some digital PLL ICs (more
> specifically the one's from AnalogDevices. It seems as if they've got some
> pretty neat stuff.) As I mentioned in my previous mail: I want to lock a
> GPSDOs 10MHz to a 100MHz OCXO using some sort of PLL. I find the PLL ICs
> convenient because they've got everything that is needed already built-in.
> Also, the phase detector and dividers are all optimised for low jitter. 
>
>  
>
> Can anyone give me some pointers regarding this? If I need a low noise
> 100MHz output, is the digital PLL and a 100MHz OCXO a good choice? I guess
> that analog PLL techniques are better, but is it worth all that effort?
> Maybe I should look at PLL ICs from other manufacturers?
>
>  
>
> Also, I'm slightly worried about the thermal instabilities inherent in the
> analog loop filter that is required by these PLL ICs. Has anyone
> successfully chased the charge pumps output through a digital filter? Or, is
> there a reason why this isn't done?
>
>  
>
> Regards,
>
>  
>
> Stephan.
>
>  
>
>    
>
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>
>   
Stephan

You may find it instructive to look at the link below where an ultralow 
noise 100Mhz oscillator is phase locked to an ultralow noise 5MHz 
oscillator using analog techniques of course.

http://www.wenzel.com/documents/ulnplls.htm

Bruce



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