AM-PM distortion caused by transistor´s signal-dependent input impedance

AM-PM distortion causes spectral regrowth in RF transmitters with modulated signals. One reason for AM-PM is the fact that signal-dependent transistor input capacitance pulls the frequency response of the input matching network and causes phase shift already at the input of the transistor. This paper studies the Miller capacitance effect in most common fixed-supply and supply modulated power amplifier topologies and typical matching networks, and shows that the signal-dependent input capacitance can cause significant AM-PM distortion.