[time-nuts] Square to sine wave symmetrical conversion
Charles Steinmetz
csteinmetz at yandex.com
Tue Jul 28 15:26:58 UTC 2015
Jerry wrote:
>I don't understand why when there is already a clean crystal current in
>the circuit, someone wouldn't want to take advantage of that signal and
>use that rather than add filters and poor biasing to the mix to claim that
>something can be done when we are talking about ideal situations where
>the lowest phase noise is desired.
It was I who originally described the "high harmonic" oscillator, so
I'll respond. I didn't suggest that you'd *want* to do that. You
said you couldn't even imagine how one would build an oscillator with
high harmonics, and I detailed one way. And while it's not the most
promising way to design a low-PN oscillator, it *is* a design that
has been used in many commercially produced oscillators over the years.
And there are reasons for using at least some features of the design
-- it is very robust over changes in component values and
characteristics, so the designer can be confident that thousands can
be made and they will all oscillate and have a predictable output
amplitude. This is not always the case with low-distortion designs
that have very little excess gain. Remember, while time-nuts and
hams can select components and tweak every oscillator they make
individually, manufacturers who are turning them out in quantity for
sale at a reasonable price have more limited options. Finally, it is
not always convenient to tap the resonator current directly, and
where it is possible the need to avoid loading the resonator may
compromise noise performance.
So -- I was not suggesting that the architecture I described is the
best way (or even a good way) to make a low-PN oscillator, but there
are reasons why it has, nevertheless, been used by the designers of
many commercial products.
Best regards,
Charles
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