In traditional hi-fi systems, the specifications of audio amplifiers emphasized audio quality, but paid less regard to the level of power losses. As the portable hi-fi sector of the audio industry has grown, however, the shortcomings of traditional amplifier devices – in particular, their inefficiency – have come to the fore.
Traditionally, audio playback equipment has used so-called Class AB amplifiers, which generate little distortion and consequently produce high audio quality. The operation of a Class AB amplifier, however, explains its relatively low efficiency: the internal voltage of the amplifier drops as the output voltage drops. The amplifier dissipates excess power across its transistors, and so as the power output to the speakers drops, the efficiency of the system declines.
In mains-powered hi-fi equipment this is not a fundamental problem; in battery-powered audio devices such as mobile phones and MP3 players, it most certainly is, as the audio amp takes a significant portion of the system’s power budget. In the case of MP3 players, the proportion of total power consumption attributable to the audio amplifier can be as high as 80 percent.
As a result, audio equipment designers have been looking for enhancements to the Class AB topology. The question that this article addresses is, are worthwhile power savings achievable through implementing a newer technology such as Class G or Class H? And if a system designer adopts a Class G or Class H amplifier, are the differences in power consumption between different implementations of Class G or Class H large enough to affect the overall power budget?
This article, which originally appeared at EE Times-Europe (Analog) , examines these questions. It is presented as a pdf file, (no registration required); to read it, click here.
About the authors
Horst Gether is Product Manager, Consumer and Communications Business Unit; Herbert Lenhard is a Design Engineer in CON MS Design Department; and Helmut Theiler is a Design Engineer in CON Backlight Design, all with austriamicrosystems.