Abstract-Modern transmitters usually have to amplify and transmit signals with simultaneous envelope and phase modulation. Due to this property of the transmitted signal, linear power amplifiers (class A, B, or AB) are usually used as a solution for the power amplifier 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 E) with a highly efficient envelope amplifier in order to obtain a linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a multilevel converter in series with a linear regulator. The multilevel converter is implemented by employing voltage dividers based on switching capacitors. The implemented envelope amplifier can reproduce any signal with a 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, the implemented prototypes have up to 20% higher efficiency than linear regulators used as a conventional solution.

In this paper, implementation and testing of non-commercial GaN FET in a simple buck converter for envelope amplifier in ET and EER transmission techniques has been done. Comparing to the prototypes with commercially available EPC1014 and 1015 GaN FETs, experimentally demonstrated power supply provided significantly better thermal management and increased the switching frequency up to 25MHz. 64QAM signal with 1MHz of large signal bandwidth and 10.5dB of Peak to Average Power Ratio was generated, using the switching frequency of 20MHz. The obtained efficiency was 38% including the driving circuit and the total losses breakdown showed that switching power losses in the FET are the dominant ones. This implies that minimization of the gate charge is the key issue in the optimization of the device for this kind of application