In modern telecommunication systems, the requirements for amount of transmitted data are increasing rapidly. For a better spectral efficiency complex type modulations (QAM, OFDM) are used, resulting in high PAPR signals. As a consequence, if conventional linear amplifiers (classes A, B) are used in transmitters, prominent linearity, but poor efficiency are assured. The efficiency of the transmitters can be significantly improved using some of the popular techniques: Kahn EER technique, ET technique, Doherty amplifier, Chireix's amplifier. In this paper, two different approaches in supplying power amplifier based on EER technique are presented. The same part of both envelope amplifiers (EA) is switched-capacitor based voltage divider combined with switching structure, analog multiplexer. The analog multiplexer is assisted with series linear regulator, in the first system, and with a fourth order LC filter, in the second system. Two prototypes for 10 W average output power with about 40 W peak output power are fabricated and the experimental results are compared in terms of efficiency and signal quality.

Abstract-Switch-mode technology is the common choice for high efficiency audio power amplifiers. The dynamic nature of real audio reduces efficiency as less continuous output power can be achieved. Based on methods used for RF amplifiers this paper proposes to employ envelope tracking techniques to the power supply in order to improve efficiency. A 100 W prototype system was designed. Measured results show that systems employing envelope tracking can improve system efficiency from 2% to 12%, i.e. a factor of 6. The temperature rise is strongly reduced, especially for the switching power MOSFETs where it is halved from 100• C to 50• C.

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