This paper reviews certain aspects of pulse-width modulation (PWM) and provides some new ideas and analyses. Computer simulations are used to study three-level PWM, the application of wide-band feedback from the unfiltered output stage, and dithering of the bias clock frequency. It is shown that feedback results in distortion-shaping topologies, which allow for easier design and implementation and reduce output stage errors. Some harmonic distortion is thereby introduced, and a theory is presented for the level of this distortion. Higher order modulators have somewhat increased distortion which does not agree with the static theory. PWM suffers from intermodulation between signal and bias components, and dithering the bias clock frequency helps to convert spectral tones in the base band into benign noise. The simulations indicate what level and type of dithering is effective.
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