A power efficient audio amplifier combining switching and linear techniques

Integrated Class D audio amplifiers are very power efficient, but require an external filter which prevents further integration. Also due to this filter, large feedback factors are hard to realise, so that the load influences the distortion- and transfer characteristics. The 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. A 30W version was realised. The switching part of the amplifier was integrated in a BCD process. Together with a linear part and with a loudspeaker as load, it has a flat frequency response +/- 0.3dB, a dissipation that is up to 5 times lower than a traditional class AB audio amplifier, and a distortion of <0.02% over power and frequency range.