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Document Part No. E5500-90024Ed. 1.0
This randomly fluctuating phase term could be observed on an ideal
RF analyzer (one which has no sideband noise of its own) as in
Figure
4-1.
Figure 4-1 RF Sideband Spectrum
There are two types of fluctuating phase terms. The first,
deterministic, are discrete signals appearing as distinct components
in the spectral density plot. These signals, commonly called spurious,
can be related to known phenomena in the signal source such as
power line frequency, vibration frequencies, or mixer products.
The second type of phase instability is random in nature, and is
commonly called phase noise. The sources of random sideband noise
in an oscillator include thermal noise, shot noise, and flicker noise.
Many terms exist to quantify the characteristic randomness of phase
noise. Essentially, all methods measure the frequency or phase
deviation of the source under test in the frequency or time domain.
Since frequency and phase are related to each other, all of these
terms are also related.
One fundamental description of phase instability or phase noise is
spectral density of phase fluctuations on a per-Hertz basis. The term
spectral density describes the energy distribution as a continuous
function, expressed in units of variance per unit bandwidth. Thus
(Figure
4-2) may be considered as:
S φ f ( )
S φ f ( )
Where BW (bandwidth is negligible with respect to any changes in
versus the fourier frequency or offset frequency (f).
E5500 Phase Noise Measurement System Version A.02.00
∆φ 2 rms f ( )
=
-------------------------------------------------------------------------------- -
=
BW used to measure ∆φ rms
Phase Noise Basics
What is Phase Noise?
rad 2
----------- -
Hz
S φ
4-3
4
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