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

Didier Juges didier at cox.net
Sat Dec 16 17:50:02 EST 2006


John Miles described a clean 110 MHz PLL from a 5.5 MHz source, which he 
used in his tracking generator project.
http://www.thegleam.com/ke5fx/tr503.html

It could be easily adapted to a 100 MHz output from a 10 MHz input.

An alternative to a PLL would be a frequency multiplier, if the original 
source at 10 MHz is clean.
The multiplier will increase the phase noise of the 10 MHz source in a 
more predictable way than a PLL, so if you have limited test 
instrumentation, a multiplier might be an easier implementation.

The PLL, if used to phase lock a high quality 100 MHz crystal 
oscillator, would be cleaner if tuned right, but could easily be worse 
than a multiplier, if not done right.

Didier

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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>   





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