The Efficiency/Bandwidth Trade-Off in Class-G Supply-Modulated Power Amplifiers

N. Wolff, W. Heinrich and O. Bengtsson

Published in:

Proc. 47th European Microwave Conf. (EuMC 2017), Nuremberg, Germany, Oct. 10-12, pp. 472-475 (2017).

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Abstract:

This work deals with class-G, i.e. discrete level, supply modulated systems. It is investigated how the efficiency improvement achievable through this approach depends on the maximum switching frequency of the modulator. As could be expected for high modulation bandwidths a fast class-G modulator is desirable in order to achieve maximum efficiency enhancement. However, for class-G, contrary to continuous envelope tracking systems, it is possible to operate the modulator at switching frequencies far below the modulation bandwidth and still achieve a significant efficiency enhancement. The results show that, for systems with two supply voltage levels, no further significant improvement in efficiency is obtained with modulator switching frequencies higher than 85% of the modulation bandwidth. For lower frequencies the efficiency decreases almost linearly. Furthermore, by increasing the amount of supply voltage levels from two to four at constant switching speed it is found that the bandwidth at constant efficiency can be increased by a factor of 3.4. In combination with digital predistortion no significant influence of the switching frequency on linearity is observed.

Ferdinand-Braun-Institut (FBH), Leibniz-Institut fuer Hoechstfrequenztechnik, 12489 Berlin, Germany

Keywords:

supply modulation; class-G; envelope tracking.