  The problem of the intrinsic origin of 1/f noise is considered. Currents and
signals consisting of a sequence of pulses are analysed. It is shown that
intrinsic origin of 1/f noise is a random walk of the average time between
subsequent pulses of the pulse sequence, or interevent time. This results in
the long-memory process for the pulse occurrence time and in 1/f type power
spectrum of the signal.
