[time-nuts] xtal oscillator phase noise
bruce.griffiths at xtra.co.nz
Sat Dec 29 18:03:49 EST 2007
Henk ten Pierick wrote:
> Some questions on xtal oscillator phase noise. Attached the
> measurement result of my series resonant xtal oscillator.
> It is a class A, ibias 5 mA, Ixtal 1 mArms. Transistor selected for
> low Rbb' 20 Ohm, Ft 100MHz. Reference voltage 5V from an ADR445,
> filtered with 10uF folie cap. Phase noise target -130dBc at 10Hz.
> 1. Is series resonant better or easier to engineer than parallel
> 2. Where should I have 20 dB/decade and where 30 B/decade?
> 3. Some suggestions for the next 25dB?
> 4. Is there more to learn from the attached picture?
A circuit diagram for the oscillator is required before intelligent
comment about changes can be made.
Either the crystal or the oscillator transistor may be limiting the
phase noise in the flicker region.
A different oscillator configuration may be better.
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