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4
Phase Noise Basics
What is Phase Noise?
What is Phase Noise?
4-2
E5500 Phase Noise Measurement System Version A.02.00
Frequency stability can be defined as the degree to which an
oscillating source produces the same frequency throughout a
specified period of time. Every RF and microwave source exhibits
some amount of frequency instability. This stability can be broken
down into two components:
G
long-term stability
G
short-term stability.
Long term stability describes the frequency variations that occur
over long time periods, expressed in parts per million per hour, day,
month, or year.
Short term stability contains all elements causing frequency changes
about the nominal frequency of less than a few seconds duration. The
chapter deals with short-term stability.
Mathematically, an ideal sinewave can be described by
2 π f o t
V t ( )
=
V o
sin
V o
Where
= nominal amplitude,
2 π f o t
V o
sin
= linearly growing phase component,
f o
and
= nominal frequency
But an actual signal is better modeled by
ε t ( )
V t ( )
=
Vo
+
ε t ( )
Where
= amplitude fluctuations,
∆φ t ( )
and
= randomly fluctuating phase term or phase noise.
2 π f o t
∆φ t ( )
sin
+
Document Part No. E5500-90024 Ed. 1.0
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