Method and apparatus for controlling a selectable voltage audio power output stage

Abstract

A method and apparatus for controlling a selectable voltage audio power output stage provides a mechanism for raising the selected power amplifier output voltage in time for the arrival of signal peaks to avoid clipping. Signal peaks may either be delayed by delaying an increase in volume control level or enabling signal compression for a predetermined time period, so that sufficient time is provided for the amplifier power supply to stabilize at a higher operating voltage when an increase of power supply voltage is selected. Alternatively, a signal level may be determined at an upstream source, such as a decoder or filter that provides information in sufficient advance of the arrival of the peaks, and used to control the power supply selection, so that the higher power supply voltage level is selected in advance of arrival of the signal peaks that would otherwise cause clipping at the power amplifier output.

Description

technical field [0001] The present invention relates to an audio power output stage of a consumer electronic device, and more particularly, to a control circuit for selecting a power supply voltage of an audio power stage. Background technique [0002] On battery-powered consumer audio equipment, a power output amplifier is typically used to drive a pair of headphones or speakers using battery power. The output stage of the device has a linear power amplifier which wastes power at low signal level output stages because the voltage drop of the active output transistors plus the output voltage equals the constant rail voltage of the power supply. [0003] Even though the current in the inverter is reduced at low signal amplitudes, more power is still wasted dissipating in the output transistors than is delivered to the load. Battery power in linear amplifier circuits is usually only reduced by reducing the supply voltage, which limits the available output power, and may not b...

AI Technical Summary

Problems solved by technology

The output stage of the device has a linear power amplifier which wastes power at low signal level output stages because the voltage drop of the operating output transistors plus the output voltage is equal to the constant rail voltage of the power supply

[0003] Even though the current in the inverter is reduced at low signal amplitudes, more power is still wasted dissipating in the output transistors than is delivered to the load

Battery power in linear amplifier circuits is usually only reduced by reducing the supply voltage, which limits the available output power, and may not be usable in some applications, such as the output of a power amplifier as a power amplifier must provide a Line output signal for a specific signal, such as a 600 ohm load loaded with +5dBm (-10dBm up 15dB), which requires a signal amplitude of 3V

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