Improved output spectrum of linearized class-F power amplifier for digital cellular mobile communications

Describes a class-F power amplifier with an amplitude distortion canceller for a cellular mobile communications terminal. The output spectrum of the power amplifier was calculated for a pi /4-shifted QPSK input signal. Calculated and measured spectra were in close agreement. Out-of-band emission of the power amplifier output spectrum is subject to both AM-AM and AM-PM conversion. The effects of AM-AM conversion can be mitigated by using an amplitude linearizer; however, AM-PM conversion is not compensated. Out-of-band emission levels were calculated as a function of AM-PM conversion to provide an estimation of allowable AM-PM conversion for a class-F power amplifier module. Calculations and measurement clarified that even a class-F power amplifier module having a phase variation of 10 to 15 degrees due to AM-PM conversion transmits a spectrum that satisfies the out-of-band emission standard.<
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