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About RF Cafe
Copyright: 1996 - 2024 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 World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while typing up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived... All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowl My Hobby Website: |
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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  Complete Non-Inverting Opamp Noise Figure Formula (for RS = RT)  Complete Inverting Opamp Noise Figure Formula (for RS = RT)   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 |
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