A Feed-Forward Power-Supply Noise Cancellation Technique for Single-Ended Class-D Audio Amplifiers

This paper presents a feed-forward power-supply noise cancellation technique to achieve high power-supply rejection ratio (PSRR) in single-ended class-D audio amplifiers. To show the effectiveness of the technique, it is implemented on a first-order single-ended pulse-width modulation (PWM) class-D amplifier. The implemented technique improves the PSRR from 20 Hz to 20 kHz independently of the close-loop compensator´s filter-order. The design methodology, implementation, and tradeoffs for the proposed technique are provided. The fabricated class-D audio amplifier achieves a PSRR of 83 dB at 217 Hz, THD+N of 0.0149%, and a maximum efficiency of 94.6% from a 1.8-V power supply. Experimental results show a PSRR improvement of 33 dB from 20 Hz to 20 kHz compared to a similar amplifier designed without the technique. The prototype was implemented using 0.18- μm CMOS standard technology, and occupies a total area of 0.121 mm². The total quiescent power consumption was 356 μW. The feed-forward power-supply noise cancellation technique enhances single-ended structures to achieve a PSRR performance comparable to differential architecture, and at the same time it consumes small quiescent power with a reduced active silicon area overhead.