Current-Injected Load-Modulated Outphasing Amplifier for Extended Power Range Operation
José Ángel García García, M. Nieves Ruiz, Ana Cordero, David Vegas
Abstract
In this letter, the power range to be covered with maximized efficiency by a two-way outphasing power amplifier (PA) is significantly extended, thanks to a proposed architecture with the injection of an external signal. Using a reactively terminated quadrature hybrid coupler (QHC) as nonisolating combiner, the Chireix topology is transformed into a slight variation in the load-modulated balanced amplifier (LMBA) when the auxiliary branch is activated. This combined load-modulated (LM) strategy provides a nearly resistive loading of the individual outphasing PAs over a wide power range. An appropriate output network, approximating a class-E/F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> operation of the selected GaN-HEMT device under such loading condition, leads to remarkable drain efficiency figures at deep output power back off (OPBO). Values higher than 80%, 70%, and 60% have been measured at power levels 9.5, 13.3, and 15 dB below its peak (45.7 dBm), respectively. A 5-MHz Long Term Evolution (LTE) signal with a peak-to-average power ratio (PAPR) as high as 12.65 dB has been reproduced with an average efficiency above 62% and worst-case adjacent channel leakage ratio (ACLR) of -31 dBc.