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Noise Figure (NF)

Definition - What does Noise Figure (NF) mean?

Noise figure is a metric used to indicate the quality of amplifiers. It is the decibel representation of the noise factor that determines the sensitivity of the amplifier is decreased to an incoming signal due to its internal noise. It is defined as the ratio of total output noise power to the output noise due to the input source. Noise figure indicates the noise performance of a radio frequency (RF) system. Noise figure is usually measured using standard noise generators or standard signal generators. The lower the noise figure value, the better the performance of the RF system.

Noise figure is also known as noise factor.

Techopedia explains Noise Figure (NF)

Noise figure is a numerical representation that denotes the quality of an RF system. It is closely related to the noise factor metric that is a ratio of the output noise power to the input noise from the source at standard noise temperature. In the case of resistors, it is the ratio of the noise produced by the resistor to the noise of an ideal resistor at standard temperatures.

There are various methods used to measure noise figure. Some of the prominent methods are:
  • Gain method
  • Y-factor method
  • Noise figure meter method

Noise figure acts as a yardstick to compare the performance of wireless communication systems where noise performance is necessary for smooth functioning. A high value of noise figure indicates system degradation and poor performance.

A typical RF system with cellular and ISM applications in the operating range of 400 MHz to 1500 MHz has a noise figure in the range of 0.9 dB in the low gain mode and 2.3 dB in the high gain mode. Measurement methods to measure noise figure must be chosen depending upon the application type, system gain and gain mode.

Amplifiers using semiconductor diodes like quantum mechanical amplifiers and cooled parametric amplifiers have the lowest noise figures.

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