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.
