Energy-efficient consumer device audio power output stage

摘要

An energy-efficient consumer device audio power output stage with gain control provides improved battery life and reduced power dissipation without clipping the audio output signal. A power supply having a selectable operating mode supplies the power supply rails to the power amplified output stage. The operating mode is controlled in conformity with an input audio signal level, which may be determined from a volume control setting of the device and/or from a signal level detector that determines the amplitude of the signal being amplified. The gain applied to the audio input signal is reduced for a predetermined time period when a higher output voltage of the power supply is selected, to avoid clipping the audio output signal.

主权项

1. An audio amplifier circuit for providing an output signal to an audio transducer, the audio amplifier circuit comprising:
a power amplifier having an audio input for receiving an audio input signal, an audio output for providing the output signal, and a pair of power supply rail connections; a power supply for providing a power supply voltage across the pair of power supply rail connections of the power amplifier, wherein the power supply has a select input for selecting an operating mode of the power supply, wherein in a first operating mode, the power supply voltage is equal to a first voltage, and wherein in a second operating mode the power supply voltage is substantially equal to a rational fraction of the first voltage, whereby power consumption of the power amplifier is reduced when a magnitude of the audio input signal is reduced; a control circuit for controlling the select input of the power supply in conformity with an indication of the magnitude, so that the control circuit selects the first operating mode when the indication of magnitude indicates that clipping may occur in the output signal; and a gain control circuit for controlling a magnitude of the audio input signal in conformity with the indication of the magnitude for a predetermined period after the control circuit selects the first operating mode of the power supply.