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A comparative system-level overview is given of alternative class-D amplifier architectures. The theory behind pulsewidth modulation and different modulation schemes is discussed. Topological alternatives such as open-loop versus feedback and fixed-carrier versus self-oscillating are analyzed and compared in terms of relevant characteristics, such as distortion, power supply rejection, efficiency, and electromagnetic interference. The combination of digital-to-analog conversion and class-D amplifiers is discussed. Experimental results of an integrated circuit based on a simple architecture that combines the benefits of digital input with an analog feedback loop are presented.