Class-X—Harmonically Tuned Power Amplifiers With Maximally Flat Waveforms Suitable for Over One-Octave Bandwidth Designs

Abstract

This paper proposes a new theory for harmonically tuned power amplifiers (PAs) with maximally flat waveforms, Class-X PAs. This class has been developed to achieve maximally flat waveforms. In this class, the relationship between the fundamental load impedance and the independently set second- and third-harmonic load impedances is established to maintain constant output power with constant efficiency. This relationship sets an optimum fundamental load design space when the second- and third-harmonic impedances are varied simultaneously and independently of each other. By varying the second- and third-harmonic impedances independently, higher flexibility in the design of broadband PAs is obtained. The theory of Class-X PA and its broadband characteristics were validated with an experimental design example using a Cree’s 10-W Gallium Nitride (GaN) device. This design showed a measured drain efficiency higher than 70% and output power within 3-dB variation over more than one-octave bandwidth.