Design of a High-Resolution Sigma-Delta Modulator for a Predominantly Digital Class-D Amplifier

This thesis presents a novel predominantly Digital Class-D Audio Amplifier, fully com- patible with standard BCD technologies, that features in the direct signal path a High- Resolution Sigma-Delta Modulator. The research on high-performance car audio systems has experienced a surge of interest in recent years, thanks to the spreading of new tech- nologies and the growth of the automotive sector. In this framework, the increasingly stringent market demands have led to the definition of specifications for cost efficiency, area, and performance at an ever-higher level. Indeed, by placing a high-performance sigma-delta modulator in the direct path, most of the signal processing functions are pushed towards the digital domain, thus allowing the use of scaled technologies with denser digital circuits to reduce costs and size. Additionally, most audio amplifiers aim to achieve high performance in terms of THD (Total Harmonic Distortion) and SNR (Signal-to-Noise Ratio). Therefore, a high gain to suppress noise and non-linearities is another requirement of primary importance. This work explores the design strategies and methodologies to meet these rigorous requirements, contributing to advancements in cost-effective, high-performance audio amplification. It starts with an overview of the entire architecture, followed by a detailed description of the Sigma-Delta modulator. The test chip has been designed and fabricated in 90-nm CMOS process technology and that are the results of three years of research activities that has been done in collaboration with STMicroelectronics. The conception, design, layout and testing phases are all described in detail and are supported by simulation and measurement results.