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/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, 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.
Highlights
MODERN wireless systems continuously advance in the use of spectrum-efficient modulation schemes to accommodate high-data rates within restricted frequency bands
The simplicity of its input signal splitter has made the Doherty power amplifier (PA) a more common choice than others, outphasing and the LoadModulated Balanced Amplifier (LMBA) architecture are gaining in attractiveness
The principle behind the LMBA is used for extending the power range to be covered with maximized efficiency by a two-way GaN HEMT class-E/F2 [8] outphasing amplifier, thanks to the non-isolating combining performance offered by a reactively terminated quadrature hybrid coupler (QHC) [9], [10] and the injection of an external control signal
Summary
MODERN wireless systems continuously advance in the use of spectrum-efficient modulation schemes to accommodate high-data rates within restricted frequency bands. Linear amplifiers with high power efficiency at deep OPBO need to be designed, relying on supply modulation and/or load modulation strategies [1]. An unbeatable efficiency profile may be obtained when using class-E PAs [2] In the latter, the desired active LM operation may be guaranteed over a very wide bandwidth [3]. The principle behind the LMBA is used for extending the power range to be covered with maximized efficiency by a two-way GaN HEMT class-E/F2 [8] outphasing amplifier, thanks to the non-isolating combining performance offered by a reactively terminated QHC [9], [10] and the injection of an external control signal
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