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Mixer Noise Figure
Concerns and
Measurements
Ed Cantrell
Oct. 1984




RF &.. Microwave
Measurement
Symposium
and
Exhibition

rhO- HEWLETT
~~ PACKARD




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Why Is Noise Important?

Receiver
System




Small Imperfect Signal Noisier
Signal Device
or
System




Noise limits the detection of weak signals. As a signal is passed through a device or system, noise is added, thus
degrading the signal to noise ratio. Noise figure is a measure of this degradation.




1

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Noise Figure Definition


Total Output Noise Power
F
Output Noise Power Due To Input Noise @ 290K



kTsB ~ No Na + kTsBG
r-----O_---4!Na~>------o=

..> V"
.. Zs @ Ts
..:
-==-

Na + kTsBG
F
kTsBG Ts 290K

FdB 10 log F



Noise figure is a measure of signal to noise ratio degradation of any device or system that has at least one input
and one output. It applies to systems as well as components of the system.




2

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Why Is Mixer Noise Figure Important?