Efficiency enhancement of class-F GaN power amplifiers using load modulation

In this work a 10 W GaN based class-F amplifier at 1 GHz is presented. The presented amplifier uses load modulation principle to achieve high efficiency over 11 dB output dynamic range. The output matching network is an L matching network with a tunable inductor and a tunable capacitor. The tunable inductor is based on a λ/4 impedance inverter and a switchable capacitor bank. The tunable inductor presents a short circuit for the second harmonic and an open circuit to the third harmonic; additionally together with the tunable capacitor they present the optimum working impedance for the transistor. The designed amplifier has a power added efficiency of 82% at an output power of 40 dBm and through using adaptive matching it can achieve a PAE of 60% at an output power of 29 dBm, in contrast to a PAE of only 22% in the case of using a fixed matching network.