Design of a Fully Differential Power Output Stage for a Class D Audio Amplifier Using a Single-Ended Power Supply

This paper presents a full-bridge discrete power output stage for a Class D audio amplifier using a single-ended power supply. The circuit receives a digital control signal with 5 V of amplitude and it generates a floating differential output voltage up to 20 V of amplitude from a single 20 V power supply voltage. Using as control signal a pulse density modulation (PDM) wave generated by an optimized 3 order continuous-time (CT) sigma delta modulator (Σ∆M), the system achieves a signal-to-noise-plus-distortion ratio (SNDR) of 83.1 dB, total harmonic distortion (THD) of -89 dB and a power efficiency of 92 %, while delivering 11 W over an 8-Ω load with a signal bandwidth of 20 kHz and a sampling frequency of 1.28 MHz.