Filterless multi-level delta-sigma class-D amplifier for portable applications

A 2 W filterless class-D amplifier using multi-level delta-sigma modulation is presented. LC filters consume large PCB space and add significant system cost, so filterless class-D solutions are preferred for portable applications. In this design, a multi-level, delta-sigma modulator is implemented to achieve high efficiency and high performance without the use of a filter. Although the modulator internally generates an 8 MHz clock, the average switching frequency of output signal is dynamically reduced to 300 kHz to minimize switching loss. Analog feedback from the output stages along with common-mode control yields 0.003% total harmonic distortion, and 103 dB dynamic range.