Modern transmitters usually have to amplify andtransmit signals with simultaneous envelope and phasemodulation. Due to this property of the transmitted signal, linearpower amplifiers (class A, B or AB) are usually used as a solutionfor the power amplifier stage. These amplifiers have highlinearity, but suffer from low efficiency when the transmittedsignal has low peak-to-average power ratio. The Kahn envelopeelimination and restoration (EER) technique is used to enhanceefficiency of RF transmitters, by combining highly efficient,nonlinear RF amplifier (class D or E) with a highly efficientenvelope amplifier in order to obtain linear and highly efficientRF amplifier. This paper compares two solutions for the envelopeamplifier based on a combination of multilevel converter andlinear regulator. The solutions are compared regarding theirefficiency, size and weight. Both solutions can reproduce anysignal with maximal spectral component of 2 MHz and giveinstantaneous maximal power of 50 W. The efficiencymeasurements show that when the signals with low average valueare transmitted, the implemented prototypes have up to 20%higher efficiency than linear regulator that is used as aconventional solution.
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