Oscillator Phase Noise
Oscillators inherently produce high levels of phase noise. That noise increases at frequencies close to the oscillation frequency or its harmonics. With the noise being close to the oscillation frequency, it cannot be removed by filtering without also removing the oscillation signal. And since it is predominantly in the phase, it cannot be removed with a limiter.
All well-designed nonlinear oscillators have stable limit cycles, meaning that if perturbed, the oscillator will naturally return to its limit cycle. This is depicted in the figure on the right (removed due to unknown copyright status). Here the stable limit cycle is shown in state space as a closed orbit (the ellipse). When perturbed, the oscillator responds by spiraling back into the limit cycle. However, by observing the time stamps, it is easy to see that while the oscillation returns to its stable limit cycle, it does not return at the same phase. This is because the oscillator is autonomous; it has no stable time reference. The phase is free to drift. As a result, any perturbation of the oscillator causes the phase to drift, which explains why the noise produced by an oscillator is predominantly in phase.
Read more about Oscillator Phase Noise: Oscillator Voltage Noise and Phase Noise Spectra, Oscillators and Frequency Correlation
Famous quotes containing the words phase and/or noise:
“It no longer makes sense to speak of “feeding problems” or “sleep problems” or “negative behavior” is if they were distinct categories, but to speak of “problems of development” and to search for the meaning of feeding and sleep disturbances or behavior disorders in the developmental phase which has produced them.”
—Selma H. Fraiberg (20th century)
“But what it was, alas, I cannot tell,
Because of it I had no perfect view;
But as it was, by guess, I wish it well
And will until I see the same anew.
Shadow, or she, or both, or choose you whither:
Blest be the thing that brought the shadow hither.”
—Unknown. I Heard a Noise and Wishèd for a Sight (l. 13–18)