Ripple feedback filter suitable for analog/digital mixed-mode audio amplifier for improved efficiency and stability

A new ripple feedback filter is presented for analog/digital mixed-mode amplifier (MMA) among audio applications. MMA is composed of two amplifiers: one is analog amplifier responsible for high fidelity and the other is digital switching amplifier in charge of high efficiency. To improve both total harmonic distortion (THD) and efficiency, a passive RLC filter is needed at the output side of the digital switching amplifier. A conventional filter, however, causes phase delay, which worsens current loop stability and makes the normal operation of MMA impossible. A ripple feedback filter is newly suggested to solve this problem, obtaining excellent efficiency and low THD.