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3
Phase Noise Basics
Where BW (bandwidth is negligible with respect to any changes in
the fourier frequency or offset frequency (f).
L(f) Another useful measure of noise energy is L(f), which is then directly
related to
if the modulation sidebands are such that the total phase deviation are much
less than 1 radian (
Figure 15 CW signal sidebands viewed in the frequency domain
L(f) is an indirect measurement of noise energy easily related to the RF power
spectrum observed on an RF analyzer.
Institute of Standards and Technology (NIST) defines L(f) as the ratio of the
power--at an offset (
sideband is based on a per Hertz of bandwidth spectral density and or offset
frequency in one phase modulation sideband, on a per Hertz of bandwidth
spectral density and
50
Sφ f ( )
S φ f ( )
by a simple approximation which has generally negligible error
∆φ
pk
e5505a_user_CW_sidebands_freq.ai
rev2 10/20/03
f)
Hertz away from the carrier. The phase modulation
(f)
power density in one phase modulation sideband
L f ( )
--------------------------------------------------------------------------------------------------------------------------------------- -
=
= single sideband (SSB) phase noise to carrier ration (per Hertz)
∆φ 2 rms f ( )
- - -- - -- - -- - -- - -- - -- - - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - - -
=
BW used to measure ∆φ rms
<< radian).
1
L f ( )
-- - S ∆φ f ( )
=
2
Figure 16
equals the Fourier frequency or offset frequency.
(
total signal power
rad 2
- - -- - -- - -- - -
=
Hz
S φ
versus
shows that the National
)
P ssb
----------- -
=
P s
Agilent E5505A User's Guide
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