Design For A New Class D Audio Power Amplifier

With the characteristics of high efficiency, energy conservation, digitization, small size and light weight, Class D audio power amplifier adapts to the objective needs of energy efficient portable devices and has great advantages in the field of audio analog integration. With the continuous advancement of design technology, Class D power amplifier is in higher performance. In this paper, the circuits are designed by the analysis of the characteristics of composition of Class D audio power amplifier based on CMOS technology, realization of the drive, SNR and distortion, etc. The target of this research is to design a Class D audio power amplifier for mobile applications, offering both high efficiency and high audio performance.After studying a large number of Chinese and foreign literature, the paper elaborates on the principles and characteristics of various power amplifiers and comparatively analyzes their strengths and weaknesses. On this basis Class D audio power amplifier based on the structure of SCOM is advanced in this paper. And its principles are elaborated.This paper analyzes the basic principles of traditional Class D audio power amplifier and advances a high-power and high-efficiency Class D audio power amplifier. With the structure of synchronous control oscillation modulation (SCOM), Class D amplifiers are applicable to mobile devices. An SCOM system is made of 2 COM systems, and a synchronization block. The synchronization block ensures precise double-sided 3-level modulation, by keeping the 2 COM systems in phase high frequency, while the differential structure ensures that the 2 COM systems are 180°out of phase low frequency, maximizing the voltage swing across the speaker load. After realizing the principle of SCOM, this paper discusses the principle and main points of the design of every block in Class D audio power amplifier and then make design and simulation of every block of the amplifier including operational amplifier circuit, comparator circuit, drive circuit, power output stage, etc. The OPA circuit and comparator circuit are the main points of this research. Through the repeated calculation and experiments, an operational amplifier and a comparator with good performances are advanced, which is an innovative design of this paper. Then simulation and analysis are given to them. SCOM structure without modulation filtering reduces the chip area. SCOM system circuits with a speaker of 2～10Ω+10μH are designed based on the calculation and repeated testing. Every block and the whole circuit of Class D audio power amplifier based on the structure of SCOM are designed and simulated with Spectre of Cadence, choosing TSMC 0.18um CMOS technology. The voltage of power supply is 3.3V. Simulation results show that the SCOM system circuits have a good performance, meeting the design requirements.