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A switching power amplifier (PA) architecture that offers up to 13 dB of output power back-off without any drain efficiency degradation is presented. The proposed zero-voltage-switching (ZVS) contour-based PA employs a series class-E PA in conjunction with duty cycle modulation and a proposed tunable impedance transformation network. So-called ZVS conditions that ensure ideally 100% drain efficiency are satisfied not just at peak output power, but over the 13-dB back-off range. Theoretical analyses of losses in the PA and the impedance transformation network are also presented to prove that drain efficiency actually improves with back-off. Measurement results of a 100-MHz PA built using discrete components on an FR4 printed circuit board showing drain efficiency greater than or equal to the peak efficiency (40%) at all output power levels are also presented.
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Singhal et al. (2011) studied this question.
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