A 650mW filterless class-D audio power amplifier for mobile applications in 65-nm technology

A class-D audio power amplifier in a standard 65-nm CMOS technology is designed for direct battery hook-up in a mobile phone. Special circuit techniques are used to overcome the voltage limitations of standard devices for operation at battery voltage levels of 2.7 - 4.8 V. The amplifier is based on a PWM modulator with feedback and outputs a three-level pulse width modulated power signal that eliminates the external low-pass filter and reduces the system cost. The amplifier achieves a power efficiency of 84% while delivering an output power of 650 mW with 1% THD into 8 Omega from a 3.7 V power supply.