A high efficiency class-I linear audio power amplifier(PA) with an adaptive supply is presented.Its efficiency is improved by a dynamic supply to reduce the power transistors' voltage drop.A gain compression technique is adopted to make the amplifier accommodate a single positive supply.Circuit complicity and chip area are reduced because no charge pump is necessary for the negative supply.A common shared mode voltage and a symmetric layout pattern are used to minimize the non-linearity.A peak efficiency of 80%is reached at peak output power.The measured THD+N before and after the supply switching point are 0.01%and 0.05%,respectively.The maximum output power is 410 mW for an 8Ωspeaker load.Unlike switching amplifiers,the class-Ⅰamplifier operates as a linear amplifier and hence has a low EMI.The advantage of a high efficiency and low EMI makes the class-I amplifier suitable for portable and RF sensitive applications. A high efficiency class-I linear audio power amplifier (PA) with an adaptive supply is presented. It efficiency is improved by a dynamic supply to reduce the power transistors' voltage drop. positive supply. Circuits complicity and chip area are reduced because no charge pump is necessary for the negative supply. A common shared mode voltage and a symmetric layout pattern are used to minimize the non-linearity. A peak efficiency of 80% is reached at peak output power. The measured THD + N before and after the supply switching point points are 0.01% and 0.05%, respectively. The maximum output power is 410 mW for an 8Ωspeaker load. Like switching amplifiers, the class-I amplifier operation as a linear amplifier and hence has a low EMI. The advantage of a high efficiency and low EMI makes the class-I amplifier suitable for portable and RF sensitive applications.