Abstract
This paper proposes a novel output combiner for Doherty power amplifiers with extended bandwidth. The proposed output combiner employs a resonance LC tank at the output of the peaking transistor to maintain the back-off impedance seen by the main transistor over a wide frequency band. In addition, the output combiner provides low low-frequency impedance for both the main and peaking transistors which results in improved linearizability when the amplifier is concurrently driven with dual-band modulated signals. A 20W, 30% bandwidth gallium nitride Doherty power amplifier based on the proposed topology was implemented to demonstrate the effectiveness of the output combiner. The Doherty amplifier was successfully linearized under single- and dual-band modulated excitations and achieved 42% power added efficiency when amplifying a concurrent dual-band 15 MHz WCDMA and 15MHz LTE signals with 9:4dB peak-to-average power ratio.
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