On 09/18/2010 09:48 AM, francesco messineo wrote:
Hello all,
sorry for the OT, but the electronic expertise of the group is too good :-)
I'm looking for ideas and directions (articles and so on) to realize
very good phase noise xtal oscillator, in the range 20-50 MHz for high
performance frequency conversion. I would like to understand what
circuits can be realized (not requiring too much professional and
modern equipment, test eq. from the 70s-80s is ok) and what is the
contribution of the active oscillator device, the xtal itself and the
following buffers.
Another idea that came on my mind was using digital oscillator (square
wave, cmos) and then filtering for sine output, if this makes sense
for a low PN point of view.
Is there any way to measure the close-in PN of oscillators with an
amateur setup?
First of all I think you need to quantify what you mean by "high
performance frequency conversion" and what stability measures you are
seeking as there are many degrees of excessiveness to attempt, and many
of them may be well beyond what you need. Remember, we are time-nuts... :)
You can pick up a lot on the theory and measurement side if you look at
Enrico Rubiolas material:
http://www.femto-st.fr/~rubiola/
I do recommend his book "Phase noise and frequency stability in
oscillators" which is aimed in a theoretical way on oscillators,
essentially driving in the point of what the Leeson theorem actually
means. This establish the system parameter rules for oscillator design.
Rubiola has a bunch of measurement tricks in his sleeve and those is
spread over various articles and presentations on the homepage.
Since Rubiolas focus isn't on actual oscillator-design but on theory and
practical measurement setups on oscillators you will not be satisfied
only with that.
Wenzel has a series of online articles which usually is a very good read:
http://www.wenzel.com/library1.htm
Further, fellow time-nut Bruce has collected a number of design ideas on
his pages:
http://www.ko4bb.com/~bruce/
There is naturally more, but that should get you going in about the
right direction.
Concept-wise, Leeson theorem explain how the amplifier noise in the
oscillation loop wraps itself around the frequency corner shaped by the
oscillators Q-value. Assuming that the Q-value is fixed, the phase noise
is shaped by the amounts of white and flicker noise in the amplifier.
Additional output buffer noise will then add ontop of that to form the
complete phase-noise. So good oscillator performance is tied to
achieving low white and flicker noise in amplifiers.
Additional contributions then comes from environmental and drift noise
sources, so additional care is to be expected there if long-term
stability is of interest.
For some applications isolational amplifiers is badly needed.
So, there is some initial pointers. There is much more, but should be of
some use to you.
Cheers,
Magnus
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