AM/PM Characterization of Wideband Power Amplifiers

This paper presents the linearity assessment of two state-of-the-art wideband power amplifiers, a single stage class AB and a two-way 6 dB Doherty, in terms of amplitude-to-phase-modulation (AM/PM) distortion. The simulated and measured characteristics are shown and discussed. The class AB amplifier maintains AM/PM within 6° from 1 to 4 GHz, i.e. on a 120% bandwidth, while the Doherty amplifier has similar performance from 2.2 to 2.9 GHz, i.e. on a 28 % bandwidth. This characterization campaign highlights the superior linearity of the class AB amplifier over relative bandwidths that exceed 100% but, at the same time, the potential of the Doherty amplifier to maintain very limited (within 10°) amplitude-to-phase-modulation distortion over bandwidths up to around 60 %. Both power amplifiers are well in line with the state of the art also in terms of linearity, besides output power, gain, and efficiency performance.