Design of a class G audio amplifier
Date of Issue2011
School of Electrical and Electronic Engineering
The demand for audio power amplifier in portable multimedia devices has been on a rise. For both manufacturers and consumers, power efficiency to maintain long battery lifetime, miniaturization to achieve smaller form factor and low Total Harmonic Distortion (THD) for quality sound synthesis are the key factors in choosing new audio gear. Linear amplifiers, such as Class A, Class B and Class AB amplifiers have low power efficiency. On the other hand, Class D amplifier which is switching amplifier, despite its relatively higher power efficiency, suffers from large form factor due to the external inductor. To address the above mentioned problems, an inductorless Class G power amplifier has been designed, operating with a single power supply. It is capable of driving a loudspeaker of up to 8Ω in parallel with a 220pF capacitive load while consuming quiescent current as low as 5mA. The proposed Class G power amplifier consists of the power supply unit and the switched-supply based amplifier unit. The power supply unit utilizes a switched-capacitor DC-DC step-down converter. It has a pulse-skip regulation to convert the external power supply (3.6V) into an internal supply rail with lower voltage (1.6V). Inside the switched-supply based amplifier unit, the supply control circuit selects between the external power supply and internal supply rail. The selection is based on the instantaneous input voltage information. The preamplifiers and DC control circuit adjust the DC offset of input audio signal into an optimum DC operating level. This design uses bridge-tied-load Class AB configuration in order to maximize the output power.
DRNTU::Engineering::Electrical and electronic engineering::Electronic systems