[time-nuts] Low phase noise VCO

Bob Camp lists at cq.nu
Wed Feb 10 00:35:25 UTC 2010


Hi

At 64 MHz you can go with a 3rd overtone crystal. If your temperature range is modest, you can pull it further than you would ever need to. 

You should be able to get good enough phase noise on the VCXO that you can use a pretty narrow loop. That's good news, it lets you use an IC phase detector and normal dividers. 

Bob


On Feb 9, 2010, at 6:41 PM, Nick Foster wrote:

> 
> Gentlemen,
> 
> Not being an oscillator guru, I thought I'd ask here. I'm building up a fixed-frequency 64MHz PLL oscillator which uses a 10MHz reference. The reference is a homebrew HP 10544A-based GPSDO which seems to work OK. I've built a phase comparator based on a CoolRunner-II CPLD which implements a flip-flop phase-frequency comparator just like the CMOS 4046. Seems to work great, although I haven't put it to the test yet with respect to phase noise. So all I need now is the VCO.
> 
> Right now, all I need is 64MHz to clock a software-defined radio, so I was thinking about using a VCXO. I see lots of solutions using LC oscillators, but very few using crystals because overtone crystals can't be pulled very far at all. So my question is, what type of oscillator would you recommend for this project, an overtone crystal oscillator like a Butler, or an LC oscillator? Is there a particular oscillator topology you favor, or (better yet) a schematic of one you like?
> 
> Thanks,
> Nick
> 		 	   		  
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