A power-efficient audio amplifier combining switching and linear techniques

Integrated class-D audio amplifiers are very power efficient but require an external LC reconstruction filter, which prevents further integration. Also due to this filter, large feedback factors are hard to realize, so that the load influences the distortion and transfer characteristics. The 30-W amplifier presented in this paper consists of a switching part that contains a much simpler filter and a linear part that ensures a low distortion and flat frequency response, The switching part of the amplifier was integrated in a BCD process, Combined with a linear part and with a loudspeaker as load, it has a flat frequency response +/-0.3 dB, a dissipation that is up to five times lower than a traditional class-AB audio amplifier, and a distortion of <0.02% over power and frequency range.