Stacked-Cell Power Amplifier Design based on Technology Characterization and Modeling

The continuous evolution of wireless communication, radar, and sensing systems toward millimeter-wave (mm-wave) frequencies imposes increasingly stringent requirements on Radio Frequency (RF) power amplifiers in terms of output power, efficiency, linearity, and reliability. Gallium Arsenide (GaAs) pseudomorphic high-electron-mobility transistor (pHEMT) technologies continue to offer a compelling solution for these applications due to their superior high-frequency performance, linearity, and process maturity. Nevertheless, the relatively low breakdown voltage limits the achievable voltage swing and output power in conventional power amplifier architectures. This thesis addresses these limitations through the investigation and development of GaAs-based stacked-cell power amplifier architectures. A comprehensive and experimentally validated design framework is proposed that spans device-level characterization, compact model extraction, architectural analysis, and millimeter-wave monolithic microwave integrated circuit (MMIC) design and implementation. This research begins with an extensive experimental characterization of GaAs pHEMT devices, including DC and multi-bias on-wafer S-parameter measurements, large-signal low-frequency (LSLF) characterization, and accelerated stress testing under realistic operating conditions. These measurements are used to evaluate technology robustness, dispersion effects, and nonlinear behavior, as well as extraction of accurate extrinsic and intrinsic device parameters. A systematic modeling procedure is established to derive reliable small- signal compact models appropriate for stability analysis and circuit-level design. A key contribution of this work is the comprehensive analysis and modeling of common-gate device behavior in stacked-cell configurations, emphasizing its essential function in inter-stage impedance matching, voltage distribution, stability, and bandwidth at millimeter-wave frequencies. Utilizing the validated models, a complete technology-aware design flow is developed and implemented for a 27-GHz GaAs MMIC stacked-cell power amplifier, encompassing stability network design, impedance matching, layout optimization, and electromagnetic co-simulation. In summary, this thesis establishes a rigorous modeling and design methodology for GaAs stacked-cell power amplifiers at millimeter-wave frequencies. The proposed framework provides a strong foundation for building and testing high-performance GaAs MMIC power amplifiers and demonstrates that GaAs technology remains important for future millimeter-wave RF front-end applications.