We investigate the Fourier transform of the current through a memristor when
the applied-voltage frequency is smaller than the characteristic memristor
frequency, and the memristor shows hysteresis in the current-voltage plane. We
find that when the hysteresis curve is "smooth", the current Fourier transform
has weights at odd and even harmonics that decay rapidly and monotonically with
the order of the harmonic; when the hysteresis curve is "sharp", the Fourier
transform of the current is significantly broader, with non-monotonic weights
at high harmonics. We present a simple model which shows that this qualitative
change in the Fourier spectrum is solely driven by the saturation of
memristance during a voltage cycle, and not independently by various system
parameters such as applied or memristor frequencies, and the non-linear dopant
drift.Comment: 5 pages, 3 figure