equivalent noise resistance
A quantitative representation in resistance units of the spectral density of a noise-voltage generator, given by Rn = (
Wn)/(kT0), where Wn is the spectral density, k is Boltzmann’s constant, T0 is the standard noise temperature (290 K), and kT0 =
4. 00 × 10-21 watt-seconds.
Note: The equivalent noise resistance in terms of the mean-square noise-generator voltage, e2, within a frequency increment, 
f, is given by Rn = e2/(4kT0f).