AVERAGE EFFICIENCY OF CLASS-G POWER AMPLIFIERS.

Abstract

The author describes the average efficiency characteristic of both two- and three-voltage class-G power amplifiers with a variety of signals. Class-G operation is an inexpensive yet effective means of increasing the efficiency of audio power amplifiers (PAs) and amplitude modulators. A class-G PA consists of two or more parallel-connected class-B PAs with different supply voltages. Low-voltage segments of the signal are amplified by the low-voltage component of the amplifier, thus reducing power dissipation and increasing efficiency. The average efficiency of a class-G PA depends on both the supply-voltage transition point and the amplitude distribution of the signal. Average efficiencies are computed for a number of signals that occur in audio frequency amplification, full-carrier amplitude modulation, and envelope modulation of a linear RF PA. For typical peak-to-average ratios, an ideal, two-voltage class-G PA has average efficiencies in the range of 60 to 70%, in contrast to the 35 to 40% of an analogous class-B PA.