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In communication systems, linear power amplifiers (PAs) (class A, B, or AB) are usually used as a solution for the PA stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration technique is used to enhance the efficiency of RF transmitters by combining highly efficient, nonlinear RF amplifier (class D or E) with a highly efficient envelope amplifier in order to obtain linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a combination of multilevel converter and linear regulator. The proposed solution can reproduce any signal with maximum spectral component of 2 MHz and give instantaneous maximum power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, it has up to 49% higher efficiency than an ideal linear regulator that is used as a conventional solution. Additionally, the algorithm for the optimization of the voltage levels, for the multilevel converter, is explained as well.
Date of Publication: April 2010