An 85.1% Peak Efficiency, Low Power Class H Audio Amplifier With Full Class H Operation

This paper presents a novel class H audio amplifier design that allows full class H operating region, optimizing the efficiency of the class H audio amplifier architecture. Class H audio amplifier is a class AB amplifier, with supply continuously tracks the output voltage, gaining the linearity and power supply rejection ratio (PSRR) performance of the class AB amplifier with much higher efficiency. In prior works on class H audio amplifier architecture, the supply tracking capability has always been limited by the minimum supply requirement for the class AB amplifier to operate. A novel class AB amplifier circuit with bootstrapping architecture to overcome this limitation will be introduced in this paper. The proposed class H audio amplifier is designed and fabricated in GF 55nm BCDLite process, occupying 2.01mm2 total chip area. The proposed class H audio amplifier is able to deliver 186.8mW peak output power to
$16\Omega $
audio load, while consuming 4.9mW quiescent power. It achieves the lowest A-weighted THD+N of −82dB and −81.5dB at 1kHz and 20kHz, respectively. The proposed class H audio amplifier also achieves 85.1% peak power efficiency, the highest as compared to prior works on class G and class H audio amplifiers. Furthermore, it is also shown in this paper that the efficiency at lower output power is significantly improved with the proposed class H audio amplifier architecture, making it highly suitable for audio applications with high crest factor (peak-to-average power ratio).