Doherty Power Amplifier Design in Gallium Nitride Technology Using a Nonlinear Vector Network Analyzer and X-Parameters

This paper presents a complete Doherty power amplifier design that has been developed entirely inside the circuit simulator, but using nonlinear vector network analyzer data and measured X-parameter models. A high-power nonlinear measurement setup with active load-pull capabilities is presented and used to extract X-parameters of a commercially available Gallium Nitride power transistor. From fundamental and harmonic impedance tuning of the measured X-parameter models, main and auxiliary amplifier matching networks are designed and proper splitter/combiner circuitry is developed to achieve optimum Doherty output power and power added efficiency. A first-pass design success (only one fabrication build is required to meet design specifications) is confirmed by measurements of the fabricated power amplifier.