Analysis of Dissipated Power in Envelope Amplifier Output Filters

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.