Class D Audio Power Amplifier Design

Compared with class AB audio power amplifier, class D audio power amplifier has an obvious advantage which is high efficiency. High efficiency can make the battery run much longer, and make the audio power amplifier dissipate less heat.First, the theory of all kinds of audio power amplifiers is introduced, their advantages and disadvantages are been compared. Then the theory of class D audio power amplifier is introduced emphatically. Compared with traditional modulation scheme, the filterless modulation scheme is analyzed, and finally been used in circuit.The whole circuit includes preamplifier, comparator, oscillation, drive, current reference, voltage feedback loop and thermal protection, over current protection, startup protection. The circuit and layout is designed and simulated with 0.5um CMOS process.In order to realize the filterless scheme, the circuit uses differential topology. Operational amplifiers in circuit are all differential. They output two audio signals which have invert phase. The number of PWM modulators and dive circuit are changed from one to two, so that the system can process the two audio signals which have invert phase. Preamplifier's pass band is designed to fit the audio band, filtering frequency which is higher than audio frequency. In order to improve the PSRR and THD, voltage feedback loop is applied. In order to prevent large current passing through H-bridge, dead time is introduced into drive circuit which can protect the H-bridge. The simulation results show that the system can work properly; its performance meets the design.