RF Cafe Software

RF Cascade Workbook

About RF Cafe

Copyright

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 ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:

AirplanesAndRockets.com

Try Using SEARCH

to
Find What You Need.

There are 1,000s of Pages Indexed on RF Cafe !

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**

V_{NOISE }= Noise voltage density, i.e. nV/sqrt(Hz)

I_{NOISE }= Noise current density, i.e.
pA/sqrt(Hz)

R_{S} = 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 R**_{S} = R_{T})

**Complete Inverting Opamp Noise Figure Formula****
(for R**_{S}** = R**_{T})

E_{NI} = Input noise voltage

I_{BN} = Non-inverting input noise current

I_{BI} = Inverting noise current

R_{S} = Source resistor

R_{T}
= Termination resistor

R_{F} = Feedback resistor

R_{G} = Gain setting resistor

V

I

R

k = Boltzmann's Constant = 1.380 662 x 10

T = Ambient temperature in Kelvin

Complete Non-Inverting Opamp Noise Figure Formula

E

I

I

R

R

R

R