[time-nuts] Optimal oscillator topology for diffrent frequency range

Gerhard Hoffmann dk4xp at arcor.de
Mon Feb 6 10:14:42 EST 2017


Am 06.02.2017 um 14:08 schrieb Richard (Rick) Karlquist:
> Agreed, for low phase noise FLOOR, it is imperative to
> take the signal out through the crystal.  However, for
> close in noise (say ADEV at t=1), the Driscoll has
> worked well for me.  I have been able to reach ADEV
> = 10^-11 at 100 MHz at using suitable resonators.
>
> Rick

But one won't be able to use the power right out of the crystal
for anything. So it will have to be amplified & buffered.

If you can do that without lifting the noise floor, then
you've got to ask yourself one question  :-)

Why don't I use that little wonder for the sustaining amplifier, too?

And - why do I divide the precious crystal power between the 2
amplifiers at the location where it hurts most: where the level is smallest?

When you compare the Driscoll and the Burgoon (sp??) output
coupling through the crystal, you see it is exactly the same.
One might even apply the current step up trick from Burgoon.

The current through the drains/collectors is enforced by the
crystal, operating into a near-short. Off-resonance the transistor
has complete negative feedback and no gain.

On the output side of the buffer, losing a dB or two for sustaining
the oscillation does not hurt.


A thing I do not like about the typical Colpitts is that it is never
on the series resonance of the crystal. That means that
the feedback divider is part of the resonance which increases
the number of critical parts.

In the Driscoll, the sustaining feedback is quite a wideband thing
and mostly decoupled from the sharp crystal resonance.


regards, Gerhard, DK4XP



>
> On 2/6/2017 4:35 AM, KA2WEU at aol.com wrote:
>> Not quiet, using the crystal also as filter gives much better numbers 
>> ,,,,,
>> 73 de Ulrich N1UL
>>
>> In a message dated 2/6/2017 7:30:33 A.M. Eastern Standard Time,
>> richard at karlquist.com writes:
>>
>>     I would say the 2 stage "Driscoll" oscillator is the
>>     way to go.  I have had good luck with it up to 100 MHz.
>>     The first stage has the crystal in series with the
>>     emitter, but is otherwise a grounded emitter stage.
>>     The second stage is in cascode as a grounded base.
>>     The important operating condition is that only
>>     the second stage limits.  First publications on
>>     it were in the early 1970's (search Michael Driscoll).
>>
>>     Rick Karlquist N6RK 



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