High efficiency class-I audio power amplifier using a single adaptive supply

Abstract

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 THDCN before and after the supply switching point are 0.01% and 0.05%, respectively. The maximum output power is 410 mW for an 8 speaker load. Unlike switching amplifiers, the class-I amplifier 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 Classification and Comparative Overview of CMOS Radio-Frequency Power Amplifiers

“…The duty cycle of the positive switching transistor is raised to produce the positive half of the waveform. At switching frequencies higher than 250 kHz, the Class-I amplifier is known alternatively as a "interleaved PWM amplifier" due to the interleaved behaviour of the two switching signal currents at the output [22], [27].…”