Superposition of similar single-sided RTN processes and 1/f noise
  In this paper it is demonstrated that a 1/f power spectrum appears in the process originated by the superposition of many similar single-sided RTN processes with the same relaxation time. The non-relaxed regime, the Gaussian nature and the average periodicity of the resulting fluctuation, are responsible for the generation of 1/f noise, thanks to the coincidences of these RTN processes. The decomposition of the resulting fluctuation, in a set of further single-sided RTN processes with a distribution of relaxation times, permits us to demonstrate once more the generation of the 1/f noise. 
Giovanni Zanella