An Energy-Efficient 2 × V BAT -Swing Switched-Mode Audio Amplifier With Fully Differential Single-Inductor Linear Buck-Boost Power Topology

This letter presents a fully differential single-inductor linear buck-boost power topology-based switched-mode audio amplifier. The proposed buck-boost amplifier with single-step class-D conversion can deliver higher power to a speaker by output swing from 0 to $2\boldsymbol {\times }$ battery voltage ( $V_{\mathrm{ BAT}}$ ) while improving the efficiency by up to 10% compared to the typical two-step conversion, which uses a separate boost converter. Inductor-freewheeling with a fixed de-energizing phase linearizes the control-to-voltage conversion even in the buck-boost topology. The chip fabricated in 0.18- $\boldsymbol {\mu }\text{m}$ CMOS achieves 0.006% THD+N and 87% efficiency at a maximum output power of 5.5 W with an 8- $\Omega $ speaker load.