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

摘要

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 26 dB 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 instruments. At nominal conditions, we find that the overcurrent protection circuit (for the output stage) is unexpectedly the most power-dissipative block in micropower CDAs. In this brief, we propose a novel ultralow-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 ultralow-power bang–bang CDA is designed. We show that, by employing the proposed overcurrent protection circuit, the power efficiency of the bang–bang CDA is significantly improved from 10.5% to 23.7% for a 64- load and from 1.8% to 4.7% for a 400- load.