Selectable Supply Audio Amplifier Control to Prevent Clipping
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Solution Overview
Problem
Battery-operated consumer audio devices with linear power amplifiers waste power during low signal levels due to constant power supply rail voltage, leading to inefficiency and potential clipping of audio signals, especially when required to maintain full signal level outputs.
Innovation Solution
A power amplifier circuit with a selectable power supply output voltage that adjusts based on the audio signal's magnitude, using a control circuit to lower the power supply voltage during low signal levels and stabilize at a higher voltage before signal peaks, thereby reducing power consumption and dissipation while preventing clipping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the power supply voltage is kept constant at maximum level, then the amplifier can maintain full signal level output capability, but power consumption and power dissipation increase significantly
Solution Approach 1:
The power supply voltage is made dynamically adjustable rather than fixed. The control circuit continuously monitors the audio signal level and adjusts the power supply voltage accordingly - using maximum voltage when high output power is needed and reducing voltage when signal levels are low, thus resolving the contradiction between maintaining power capability and reducing power consumption
Solution Approach 2:
The power supply voltage parameter is changed dynamically based on signal level requirements. By varying this critical parameter from maximum to reduced levels, the system can maintain full output capability when needed while consuming less power during normal operation, directly addressing the technical contradiction
2Loss of energy
If the power supply voltage is lowered to reduce power consumption, then power dissipation decreases, but the amplifier may clip the audio signal at high signal levels
Solution Approach 1:
A control circuit provides feedback by monitoring the audio signal level and using this information to adjust the power supply voltage. This closed-loop feedback mechanism ensures the power supply voltage is always appropriate for the current signal level, preventing clipping while minimizing power dissipation
Solution Approach 2:
The control circuit proactively adjusts the power supply voltage in advance of signal peaks by monitoring signal level trends. This preliminary action ensures sufficient voltage headroom is available before high-amplitude signals arrive, preventing clipping while maintaining low power dissipation during normal operation
3Device complexity
If a linear power amplifier is used, then simple circuit design is achieved, but power is wasted during low signal level outputs
Solution Approach 1:
The power supply voltage parameter is dynamically changed based on signal level, transforming the simple linear amplifier into an adaptive system. This single parameter change resolves the power waste issue without requiring complex amplifier topology changes, maintaining relative design simplicity while eliminating the contradiction
Data Source
AI summary
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.