Design and simulations of a class D audio amplifier featuring novel digital modulations

In recent years there has been an increasing demand of portable electronic devices, from mobile phones to personal computers, from MP3 players to hearing-aid systems which have to be smart, light and low-power consuming. As far as the power dissipation is concerned, the audio power results one of the most critical. For this reason, a lot of research has been carried out to and out solutions that allow to reach very high power efficiency, without reducing the audio quality. In fact, even if traditional linear amplifier classes (e.g. A, B, AB) can reach high performance in terms of audio quality, with low distortion, they have severe limitations in terms of effciency, dissipated heat and weight (in particular for high power levels). Class D audio switching amplifiers, proposed in 1958, can reach 100% power efficiency (in real cases about 80%-90%) against 75% of class AB (in real cases about 30%-40%). The increase in power effciency has an impact both in terms of less heat generation and lower weight, increasing the portability of the system in which they operate. Moreover, advances in research and development of semiconductor technology have allowed the integrability of those amplifier circuits and higher switching frequency. One of the main drawback of class D amplifiers is the generation of higher distortion level of amplified signal with respect to that of traditional classes. To reduce this distortion, solutions have been proposed most of which exploit the features of closed loop negative feedback. In this context, control laws implemented through digital programmable circuits it is preferred to analog implementations both in terms of noise immunity and in terms of higher flexibility since the control can be specified in terms of software. In this thesis, a class D audio amplifier has been designed taking advantage of the most recent state of the art architectural and technological solutions. In particular, the modulation section is analyzed in detail, highlighting the limitation of this section implemented in digital way by means of DPWM and DDPWM and overcome them by means of a new proposed modulator that is a combination of DPWM and DDPM modulation techniques. The models of the open- and closed-loop amplifier, implemented in MATLAB, are designed under some specifications and a rigorous methodology design for closed-loop system is shown. Then, a comparison among the proposed solutions is done, highlighting the differences among them in terms of distortion, noise and speed, which influence the efficiency of the overall system. Finally, a possible physical implementation is suggested using GaN and MOS transistors, to compare in future the effect of different technology on the experimental performances of a class D amplifier.