[time-nuts] Low phase noise VCO
bistromat at hotmail.com
Wed Feb 10 21:08:16 UTC 2010
That's a great suggestion, Ulrich. Thanks. It took all of five minutes to implement in VHDL, and looks great.
I also found Fox's "Xpresso" line of miniature synthesized VCXOs, and the numbers look pretty compelling. CMOS output, too. And, the best part, they're available off-the-shelf. Does anyone have experience with these in low-noise applications? They're ludicrously expensive (Digikey lists them for $47/ea in short qty), but if I can get some samples from Fox, it'll save me a lot of grief.
I'll let you all know how it works out, and Don, if I get samples and they work OK I'll mail you some.
> From: df6jb at ulrich-bangert.de
> To: time-nuts at febo.com
> Date: Wed, 10 Feb 2010 09:02:30 +0100
> Subject: Re: [time-nuts] Low phase noise VCO
> altough you have been asking for advice for the VCO I would like to draw
> your attention on how you can improve your phase detector. Edge-triggered
> phase detectors are not bad, the even can work as frequency detectors if you
> are far from lock and help you to gain lock where a XOR would not. However,
> once you are CLOSE to a phase lock, a simple XOR makes the better phase
> detector with less phase noise. There is a VERY easy circuit that marriages
> the best of both worlds. Google for the AD9901 frequence/phase detector and
> mimic their schematic of the first page into your CPLD. Have done this with
> different CPLDS from XILINX and ALTERA and has always worked very well for
> me in terms of frequency locking range and low phase noise.
> Best regards
> Ulrich Bangert
> > -----Ursprungliche Nachricht-----
> > Von: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] Im Auftrag von Nick Foster
> > Gesendet: Mittwoch, 10. Februar 2010 00:41
> > An: time-nuts at febo.com
> > Betreff: [time-nuts] Low phase noise VCO
> > 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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