Current-injected load-modulated outphasing amplifier for extended power range operation

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 injection of an external signal. Using a reactively terminated quadrature hybrid coupler (QHC) as non-isolating combiner, the Chireix topology is transformed into a slight variation of the Load-Modulated Balanced Amplifier (LMBA) when the auxiliary branch is activated. This combined 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/F2 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 dB, 13.3 dB and 15 dB below its peak (45.7 dBm), respectively. A 5 MHz 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.