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7
Residual Measurement Fundamentals
What is Residual Noise?
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.
The noise mechanisms
Residual noise is the sum of two basic noise mechanisms:
• additive noise
• multiplicative noise
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
Noiseless
E5505a_add_noise_comp
27 Feb 04 rev 1
Figure 144 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
202
Device under
Source
source
Figure
test
RF noise added
to the signal
RF noise around
the signal frequency
145.
Figure
144.
Agilent E5505A User's Guide
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