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In signal processing, phase noise is the frequency-domain representation of random fluctuations in the phase of a waveform, corresponding to time-domain deviations from perfect periodicity . Generally speaking, radio-frequency engineers speak of the phase noise of an oscillator, whereas digital-system engineers work with the jitter of a clock.
Thus, noise at f 1 is correlated with f 2 if f 2 = f 1 + kf o, where k is an integer, and not otherwise. However, the phase produced by oscillators that exhibit phase noise is not stable. And while the noise produced by oscillators is correlated across frequency, the correlation is not a set of equally spaced impulses as it is with driven systems.
Jitter period is the interval between two times of maximum effect (or minimum effect) of a signal characteristic that varies regularly with time. Jitter frequency, the more commonly quoted figure, is its inverse. ITU-T G.810 classifies deviation lower frequencies below 10 Hz as wander and higher frequencies at or above 10 Hz as jitter. [2]
Reference clock jitter translates directly to the output, but this jitter is a smaller percentage of the output period (by the ratio above). Since the maximum output frequency is limited to /, the output phase noise at close-in offsets is always at least 6 dB below the reference clock phase noise. [6]
The variance between these phases is called tracking jitter. Ideally, the static phase offset should be zero, and the tracking jitter should be as low as possible. [dubious – discuss] Phase noise is another type of jitter observed in PLLs, and is caused by the oscillator itself and by elements used in the oscillator's frequency control ...
Leeson's equation is an empirical expression that describes an oscillator's phase noise spectrum.. Leeson's expression [1] for single-sideband (SSB) phase noise in dBc/Hz (decibels relative to output level per hertz) and augmented for flicker noise: [2]
Jitter is a form of phase noise that must be minimised in applications such as radio receivers, transmitters and measuring equipment. When a wider selection of clock frequencies is needed the VCXO output can be passed through digital divider circuits to obtain lower frequencies or be fed to a phase-locked loop (PLL).
Distributing power with solid plane layers to limit power supply noise; Adding a pre-emphasis filter to the transmitter driving cell [13] Adding an equalizer to the receiving cell [13] Improved clock and data recovery (CDR) circuitry with low jitter/phase noise [14] Each of these fixes may possibly cause other problems.