Smooth memory effects are not usually harmful to the linearity of the PA itself. A
phase rotation of 10º to 20º or an amplitude change of less than 0.5 dB, as a function
of modulation frequency, has no dramatic effect on the linearity of the device,
There are two memory effects: electrical and thermal.
Electrical memory effects are produced by non-constant node impedances within
frequency bands as DC, Fundamental, and Harmonics. Most of these effects are
generated by frequency dependent envelope impedance, and those within the DC
band are the most harmful, because bias impedances are strongly frequency
dependent.