Before revision: The power spectral density of the noise is expressed in terms of the temperature (in kelvins) that would produce that level of Johnson–Nyquist noise, thus: where: is the noise power (in W, watts) is the total bandwidth (Hz, hertz) over which that noise power is measured is the Boltzmann constant ( 1.381×10−23 J/K , joules per kelvin) is the noise temperature (K, kelvin) Thus the noise temperature is proportional to the power spectral density of the noise, .
After revision: The power spectral density of the noise is expressed in terms of the temperature (in kelvins) that would produce that level of Johnson–Nyquist noise, thus: where: is the noise power (in W, watts) is the total bandwidth (Hz, hertz) over which that noise power is measured is the Boltzmann constant ( , joules per kelvin) is the noise temperature (K, kelvin) Thus the noise temperature is proportional to the power spectral density of the noise, .