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Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2016
Webmaster:
Kirt Blattenberger,
 BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

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Opamp Noise Figure

These equations calculate the noise figure of an opamp using parameters provided by vendors at the operating frequency and gain configurations. Be sure to note units both for the input parameters and for the equations, or you will end up with really bad results. I originally got these formulas from an engineering desk reference, but a source accessible by everyone is "Noise Analysis for High-Speed Op Amps," by Texas Instruments (see page 9).

Approximation Formula

VNOISE = Noise voltage density, i.e.  nV/sqrt(Hz)
INOISE = Noise current density, i.e.  pA/sqrt(Hz)
RS = Source resistance, i.e. 50 Ω
k = Boltzmann's Constant = 1.380 662 x 10-23 J/K
T = Ambient temperature in Kelvin


Opamp Noise Figure equation formula - RF Cafe



Complete Non-Inverting Opamp Noise Figure Formula (for RS = RT)

Opamp Noise Figure equation formula - RF Cafe



Complete Inverting Opamp Noise Figure Formula (for RS = RT)

Opamp Noise Figure equation formula - RF Cafe
Opamp Noise Figure equation formula - RF Cafe


ENI = Input noise voltage

IBN = Non-inverting input noise current

IBI = Inverting noise current

RS = Source resistor

RT = Termination resistor

RF = Feedback resistor

RG = Gain setting resistor

Related Pages on RF Cafe
- Amplifier Design Resources
- Opamp Noise Figure
- Operational Amplifiers (Opamps)
- Amplifier Vendors - RF / Operational / Log Video
- Amplifier Vendors - Tubes, Vacuum, Klystron, TWT
- Amplifier Vendors - Discretes
- RF & Analog Amplifier Vendors - Packaged & MMIC
- NEETS - Introduction to Amplifiers
- Power Amplifier Linearization Using Diode On Voltage
- GSM Handset Power Amplifier Control Loop Design