Hi
In general the synthesized parts are not real low noise. You can do better
with $5 worth of parts and some tinkering time.
Bob
--------------------------------------------------
From: "Nick Foster" <[email protected]>
Sent: Wednesday, February 10, 2010 4:08 PM
To: <[email protected]>
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.
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
>
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