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This letter describes a power amplifier (PA) with high linearity based on the envelope elimination and restoration (EER) technique. PAs based on this technique are composed of a highly efficient nonlinear PA (class E) that performs phase modulation and a wide bandwidth envelope amplifier that supplies the nonlinear PA and has to inject the envelope through power supply modulation. The design of the envelope amplifier is a complicated task due to the tradeoff between demanded high efficiency and very wide bandwidth. In order to obtain a reasonably high efficiency and very wide bandwidth, a solution based on the multilevel converter in series with a linear regulator is proposed. It provides up to 100 W of peak power and tracks sine waves up to 2 MHz. The class E amplifier has been optimized for high-efficiency (near 85%) and high-frequency (120 MHz) operation. The experimental results presented in this letter validate the proposed solutions for the envelope and phase amplifier, demonstrate that the implemented EER PA can handle up to 100 W of peak power, and highlight its high linearity (around 40 dB of attenuation of the intermodulation products) and high efficiency (up to 25% less power losses than an ideal class B amplifier).
Date of Publication: Jan. 2012