PWM Amplifier Control Loops with Minimum Aliasing Distortion
PWM class-D audio power amplifiers contain typically a control loop filter network and a comparator producing the PWM signal. The comparator performs a sampling operation whenever it changes state. A previous paper by the author analyzed this sampling behavior from a small signal point of view. The present paper attempts to formulate a large-signal model that accounts for the non-linear effects of the sampling due to aliasing of high frequency carrier components. The model is validated using simulations and a class of loop filters is presented that obtains minimum aliasing distortion thanks to the use of quadrature sampling. Finally, measurement data are presented for real applications using the principles described.
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