Design of RF/microwave integrated circuits in GaN MMIC technology (1 GHz - 12 GHz) - Construction of a GaN MMIC power amplifier with active load modulation and dynamic bias
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Based on the concept developed by Morten Olavsbråten at the department of Electronics and Telecommunications at NTNU, an amplifier based on a modification of the Doherty amplifier is designed in Keysight Advanced Design System (ADS) with GaN MMIC models for all components except splitter and load. The goal of the amplifier is to remove the quarter-wave transmission lines to increase its bandwidth. Envelope tracking is used to ensure the same characteristic efficiency curve as the Doherty amplifier, and a linear voltage tracking scheme is found to produce the best combination of efficiency and gain. The parasitics of the transistor is included in the network designs to ensure increased control of the impedances observed by the transistors current source. The initial bandwidth goal is 800 MHz with center frequency at 2.4 GHz, but the final result yields a bandwidth of 1.2 GHz spanning from 1.6 GHz to 2.8 GHz. Drain efficiency lies above $40\%$ efficiency for a power backoff of 13dB, for all frequencies.