A comparison of flicker noise and shot noise on a hot cathode

A simple formula is constructed that gives an immediate assessment of the relative importance of flicker noise and shot noise on a hot cathode, which is operated in the temperature limited regime. Its synthesis is guided by previous measurements of emission noise on various cathodes. Other than the system parameters that are specified by the applications, the formula depends only on the "crossover frequency," at which the flicker noise spectral density is equal to the shot noise spectral density.