[time-nuts] Low phase noise VCO
lists at cq.nu
Wed Feb 10 21:40:41 UTC 2010
In general the synthesized parts are not real low noise. You can do better
with $5 worth of parts and some tinkering time.
From: "Nick Foster" <bistromat at hotmail.com>
Sent: Wednesday, February 10, 2010 4:08 PM
To: <time-nuts at febo.com>
Subject: Re: [time-nuts] Low phase noise VCO
> 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
>> are far from lock and help you to gain lock where a XOR would not.
>> 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
>> the best of both worlds. Google for the AD9901 frequence/phase detector
>> mimic their schematic of the first page into your CPLD. Have done this
>> different CPLDS from XILINX and ALTERA and has always worked very well
>> 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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