Design and implementation of a 1 GHz GaN HEMT class-F power amplifier for transistor model evaluation

Besides linearity, gain and output power, efficiency is an important issue for power amplifiers in wireless communication systems. Since power amplifiers are components which consume the major power in the entire system, improving power amplifiers\´ efficiency leads to significant improvement of the system\´s efficiency. One of the amplifier design concepts for efficiency enhancement is class-F power amplifier where the power transistor is operated as a switch. In order to obtain high power, the output voltage of the "off state should be high, whereas the current should be zero. Thus, it is advantageous to use a power device with high breakdown voltage. This property is offered by power devices based on wide-bandgap semiconductor materials e.g. SiC, InP or GaN with GaN transistors as the most wide-spread and promising high frequency power devices. In addition GaN-based transistors offer also other advantages e.g. high power density, high frequency and temperature of operation, wide bandwidth, high output impedance for easy matching, etc.. This paper proposes a high efficiency class-F power amplifier based on GaN HEMT with the operating frequency of 1 GHz. The optimum load and source impedance for the proposed class-F power amplifier are determined using load- and source pull simulations. The output matching network was designed including harmonic resonators up to 5^th harmonic. During the design process, the parasitics of the device\´s package are also taken into account in order to achieve the optimal class-F load condition at the intrinsic drain of the transistor inside the package. The fabricated class-F power amplifier achieved a maximum power added efficiency (PAE) of 68.45%. Simulation and measurement results have shown good agreement which confirms the accuracy of the device model under realistic condition of operation as a power device for a class-F power amplifier.