A low-voltage fully-monolithic ΔΣ-based class-D audio amplifier

This paper presents a single-chip digital audio amplifier based on a delta-sigma (DeltaSigma) modulator and a power-efficient switching (class-D) output-stage without intermediate filtering. Fabricated in a 0.18-mum standard digital CMOS process, this audio amplifier can operate from a single power-supply of 1.8V down to 1V, without significant change in performance. It has a measured total-harmonic-distortion (THD) at the speaker terminals of less than 0.07%, with a dynamic range (DR) of 85dB. An efficiency of 76% can be achieved with a 4.3-Omega speaker. The maximum output power is 350mW (rms) from a single 1.8-V power-supply, and the stand-by power consumption is only 7.5mW (load connected). This work demonstrates the feasibility of implementing class-D amplifiers with a high-end audio performance in low-voltage environments.