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8
Residual Measurement Fundamentals
What is Residual Noise?
What is Residual Noise?
The Noise
Mechanisms
8-2
E5500 Phase Noise Measurement System Version A.02.00
Residual or two-port noise is the noise added to a signal when the
signal is processed by a two-port device. Such devices include:
amplifiers, dividers, filters, mixers, multipliers, phase-locked loop
synthesizers or any other two-port electronic networks. Residual
noise is composed of both AM and FM components.
Residual noise is the sum of two basic noise mechanisms:
Additive noise
Additive noise is the noise generated by the two-port device at or
near the signal frequency which adds in a linear fashion to the signal.
See
Figure
8-1.
Figure 8-1 Additive Noise Components
Multiplicative Noise
This noise has two known causes. The first, is an intrinsic, direct,
phase modulation with a 1/f spectral density and the exact origin of
this noise component is unknown. The second, in the case of
amplifiers or multipliers, is noise which may modulate an RF signal
by the multiplication of baseband noise with the signal. This mixing
is due to any non-linearities in the two-port network. The baseband
noise may be produced by the active device(s) of the internal
network, or may come from low-frequency noise on the signal or
power supply. See
Figure
8-2.
Document Part No. E5500-90024 Ed. 1.0
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