Design Of A Mono Filterless Class-D Audio Power Amplifier

Compared with the traditional analog-audio power amplifier, the class-D type based on switching mode has been greatly developed in the fields of high power and portable audio and video devices. The class-D audio power amplifier has obvious advantages such as high efficiency, low power and small volume, etc. So it is significant to design a class-D audio power amplifier with the features of high power, low distortion and high efficiency.Upon the analysis of the basic principles and the design factors of the class-D audio power amplifiers, a mono class-D audio power amplifier is designed. A constant gm PWM comparator with Rail-to-Rail input stage is proposed which effectively enhances the precision while ensures the speed. Designed with a full differential, high gain and wide output swing operator amplifier, it obtains high accuracy and antinoise ability. The design adopts voltage negative feedback technology allowing the system to achieve a higher power supply rejection and reducing the output error introduced from power MOS and the harmonic distortion. The circuit uses novel filterless PWM modulation and full-bridge output mode which can simplify periphery system design and achieve wide output swing. In addition, some protection circuits are integrated in the chip, such as over temperature, short circuit protection and under voltage lock circuit to prolong the chip lifespan.Finally, the design is schemed out based on 0.35μm 5V CMOS process. The simulation and verification of the whole chip have been completed using the Cadence tools and the results indicate that performances reach the expectation, both in function targets and electrical characteristics. The working frequency of the chip is 250 KHz, quiescent current is 2.5mA and shutdown current is less than 1μA. On the condition of 5V supply voltage and 4Ωload, the highest output power is 2.5W and the efficiency is 88%. The area of the chip is 1.54×0.59 mm2 and it is being taped out.