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.
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)