A Novel 3D Filter-less Class-D Audio Amplifier with Stereo Enhancement

Abstract This paper presents a novel 3D filter-less class-D audio amplifier with the stereo enhancement structure. The principle of this stereo enhancement scheme has been analyzed. It shows that the amplifier with this proposed circuit has a better live effect than the traditional class-D audio amplifiers. In this amplifier, the input audio signal from one channel can be amplified in two channels at the same time by way of cross-coupling. The ratio of gains in the two channels also can be adjusted by changing the external resistance, which improves the stereo effect. A practical implementation in the SMIC CMOS 0.18-μm process has been done to validate the theoretical results. When a sine signal with 1 kHz frequency and 100 mV amplitude is applied in one channel and a DC applied signal in the other, the amplifier demonstrates a gain difference of 9.4 dB. A double-sided natural sampling PWM is used in the proposed class-D amplifier to eliminate low-pass filter. The experimental result shows that the amplifier can deliver 2.5 W × 2 into 2 Ω loads at 3.3 V power supply and the THD + N is less than 0.1% without the external filters.

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