A Comparative Analysis of Two Approaches in Envelope Tracking Power Supplies for Satellite Applications

In modern telecommunication systems, the requirements for amount of transmitted data are increasing. In order to transmit as much information as possible for a given spectral band, both amplitude and phase modulation are applied. The main power consumers in transmitters are power amplifiers(PA), placed in the output stage. During the last decade, a lot of efforts have been invested in optimization of the efficiency of RF power amplifiers. One of notable techniques is Kahn’s envelope and restoration (EER) principle, where highly efficient envelope tracker and non-linear RF amplifier (e.g. class E, F) are combined. In this paper, two different approaches in envelope tracking are presented. The first approach is based on an analog multiplexer and a linear regulator in series, while the second tracker consists of PWM controlled switches and the fourth order output filter. Both trackers are supplied with highly efficient (96%) switch-capacitor based multilevel power converter, which acts as a voltage divider. Additionally, the comparison between two prototypes of the first approach, with Si and GaN based transistors is presented. Experimental results show that peak efficiencies are 73% (Si) and 75% (GaN), in the case of a 5 MHz 64QAM reference signal, with 10 W average output power. For the second approach, different filter prototypes are analysed. Moreover, their impact on envelope signal processing is backed up with the simulation results and the experimental results for tracking of a 2 MHz 64QAM reference are presented, with 78% achieved efficiency (Si technology) and 9 W average output power.