Switching power amplifiers need an analogue low-pass filter between the power transistors and the speaker to prevent HF switching noise to enter the speaker. Cancellation of the non-linearities, as well as the (load dependent) frequency transfer of this filter is desired, but traditionally very difficult because of stability problems with filter-output feedback. A switching power amplification topology is presented which offers total control over the output filter dynamics and cancellation of the filter characteristics. The proposed amplifier uses a hysteresis circuit with a high-bandwidth capacitor-current feedback as PWM modulator. The output filter is thus an integral part of the modulator which dramatically improves control of the output. The result is a very high fidelity amplifier which is unconditionally stable, regardless of the load.
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