Efficient MMIC Power Amplifier Implementations for Applications Beyond 100 GHz

Licentiatavhandling, 2025

The rapid increase in worldwide wireless data traffic underscores the need for advancements in wireless communication infrastructure. Millimeter Wave (mm-wave) frequencies provide abundant and less crowded spectrum resources for these networks. However, designing energy-efficient Power Amplifiers (PAs) at these frequencies remains a challenge due to increased power losses and the performance limitations of transistors.

In this thesis, we present the design and implementation of energy-efficient PAs for mm-wave frequencies using a commercial 0.1 μm GaAs pHEMT process, specifically targeting telecommunications bands between 100 GHz to 114 GHz. Starting from fundamental PA design principles, various power-combining techniques were investigated. A balanced PA demonstrating competitive performance relative to state-of-the-art designs was developed, achieving 24.1dBm saturated output power, 18.2 dB gain, and 11.9% power-added efficiency. Additionally, a non-uniform distributed power amplifier employing multi-branch combining was designed, exhibiting a small-signal gain exceeding 20 dB from 107 GHz to beyond 116 GHz.

To further enhance performance, a dynamic gate biasing technique was introduced and initially validated on an 80 GHz PA, improving average energy efficiency at the spectral emission mask limit from 4.9% to 7.4% and increasing average RF output power by 1.7dBm, surpassing traditional digital pre-distortion techniques. A novel integrated dynamic gate bias circuit was subsequently implemented in a single Monolithic Microwave Integrated Circuit (MMIC), dynamically adjusting gate voltage based on instantaneous input power. Quasi-static simulations confirmed significant improvements, increasing maximum RF output power from 19.14dBm to 20.81dBm for a 4QAM signal and improving energy efficiency from 10.2% to 12.5%. These findings demonstrate the effectiveness of dynamic gate biasing in optimizing efficiency and output power in advanced mm-wave PAs.

Overall, this work demonstrates the potential of MMIC implementations using 0.1 μm GaAs pHEMT technology for energy-efficient PA design in mmwave applications. These findings support the development of high-performance PAs for modern wireless systems, particularly those operating with signals that exhibit a large dynamic range.