An Ultralow-Power Overcurrent Protection Circuit for Micropower Class D Amplifiers

Abstract

Although Class D Amplifiers (CDAs) are highly advantageous over their linear amplifier counterparts in terms of power-efficiency, their power-efficiency remains undesirably low at nominal operation conditions where the output power is ~26dB lower than its peak output power (due to the large crest factor of the audio/speech signal and headroom for adjustment). This is particularly the case for power-critical micropower applications such as hearing instrument. At the nominal conditions, we find that the overcurrent protection circuit (for output stage) is unexpectedly the most power dissipative block in micropower CDAs. In this paper, we propose a novel ultra-low-power overcurrent protection circuit which features 67% lower power dissipation compared to conventional overcurrent protection circuit without compromising the IC area. To further verify the advantages of the proposed overcurrent protection circuit, an ultra-low power Bang-bang Class D amplifier is designed. We show that by employing the proposed overcurrent protection circuit, the power-efficiency of the Bang-Bang Class D amplifier is significantly improved from 10.5% to 23.7% for a 64 load and from 1.8% to 4.7% for a 400 load. 