A Fixed-Frequency Sliding-Mode Controller for Fourth-Order Class-D Amplifier

Since the parasitic voltage ringing and switching power losses limit the operation of active devices at elevated frequencies; therefore, a higher‐order inductor‐capacitor (LC) filter is commonly used, which offers extended attenuation above the cutoff frequency and thus, improves the total harmonic distortion (THD) of the amplifier. This paper applies the concept of integral sliding‐mode control to a fourth‐order class‐D amplifier. Two fixed‐frequency double integral sliding‐mode (FFDISM) controllers are proposed, where one uses the inductor current while the other involves the capacitor current feedback. Their equivalent control equations are derived, but from the realization viewpoint, the controller using the capacitor current feedback is advantageous and, therefore, is selected for final implementation. The performance of the proposed FFDISM controller for fourth‐order GaN class‐D amplifier is confirmed using simulation and experimental results.