Current-Injected Load-Modulated Outphasing Amplifier for Extended Power Range Operation

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
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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.