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. Nick > From: [email protected] > To: [email protected] > Date: Wed, 10 Feb 2010 09:02:30 +0100 > Subject: Re: [time-nuts] Low phase noise VCO > > Nick, > > 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: [email protected] > > [mailto:[email protected]] Im Auftrag von Nick Foster > > Gesendet: Mittwoch, 10. Februar 2010 00:41 > > An: [email protected] > > 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 > > > > _________________________________________________________________ > > Hotmail: Powerful Free email with security by Microsoft. > > http://clk.atdmt.com/GBL/go/201469230/direct/01/ > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _________________________________________________________________ Hotmail: Free, trusted and rich email service. http://clk.atdmt.com/GBL/go/201469228/direct/01/ _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
