S. Paul¹, N. Wolff¹, C. Delepaut², V. Valenta², W. Heinrich¹ and O. Bengtsson¹

Published in:

48th European Microwave Conference (EuMC 2018), Madrid, Spain, Sep. 25-27, pp. 515-518 (2018).

Abstract:

The paper addresses power dissipation within the output filter of a buck-converter-based envelope amplifier (EA) and its effect on the overall envelope tracking (ET) system efficiency. For a 57 W peak-power GaN-based ET system operating at 1620 MHz and 40 V supply, the power dissipated in the EA output filter is compared to the power loss in the entire ET system. Three different fourth-order LC low-pass filters with 10 MHz cut-off frequency are investigated regarding their load-dependent dissipated power during static and dynamic EA operation, i.e., with constant and modulated EA output voltages, for an 8 MHz OFDM-modulated RF input signal. It is found that the portion of the power dissipated in the filter constitutes a considerable part of the overall power dissipation of the ET system for a wide range of output power. Alternative filters of similar order and cut-off frequency show an estimated EA efficiency difference of up to 5% points. Furthermore, the investigations show that considering the static case alone, where the filter is loaded by a fixed impedance, may lead to totally wrong conclusions for more realistic dynamic conditions in the ET system.

Keywords:

DC-DC power converters, efficiency enhancement, envelope tracking, low-pass filters, RF power amplifiers, supply modulation.

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