Average Efficiency of Class-G Power Amplifiers

Class-G operation is an inexpensive and 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 upon 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 AF 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 percent, in contrast to the 35 to 40 percent of an analogous class-B PA.