Charge-Pump Audio Amplifier Power Supply with Dynamic Gain Control
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Solution Overview
Problem
Battery-operated consumer audio devices face inefficiencies in power amplifiers, as linear power amplifiers waste power during low signal levels due to constant power supply voltage, limiting output power and increasing dissipation, especially when maintaining full signal level requirements.
Innovation Solution
A power amplifier circuit with a selectable-voltage charge-pump power supply that adjusts output voltage based on audio signal levels, using a control circuit to generate a control signal and a gain control circuit to prevent clipping, allowing for reduced power supply voltage during low signal amplitudes, thereby conserving power and reducing dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a linear power amplifier uses a constant power supply voltage to maintain full signal level output capability, then the output power and signal level are ensured, but power dissipation increases significantly during low signal levels
Solution Approach 1:
The power supply voltage is made dynamic rather than constant. The charge-pump power supply adjusts the voltage level based on the audio signal amplitude, providing high voltage only when needed for peak signals and reducing voltage during low signal levels. This dynamic adjustment resolves the contradiction by making the power supply adapt to actual signal requirements rather than maintaining a fixed high voltage state.
Solution Approach 2:
The power supply voltage parameter is changed dynamically based on signal level detection. The system monitors audio signal amplitude and adjusts the power supply voltage accordingly, transitioning between different voltage states. This parameter change allows the amplifier to maintain full output capability when needed while reducing power dissipation during normal operation.
2Loss of energy
If the power supply voltage is lowered to reduce power dissipation during low signal levels, then energy efficiency improves, but the available output power and full signal level capability are limited
Solution Approach 1:
The power supply operates in dynamic modes rather than a fixed state. During low signal levels, the charge-pump provides reduced voltage to minimize power dissipation. When high signal levels or peaks are detected, the charge-pump switches to provide full voltage to ensure adequate output power. This dynamic operation resolves the contradiction by adapting power delivery to actual signal requirements.
Solution Approach 2:
The charge-pump power supply operates in periodic cycles, switching between low-voltage and high-voltage modes based on signal detection. The system periodically assesses signal levels and adjusts power delivery accordingly, providing full power only during necessary periods while conserving energy during extended low-signal periods.
3Loss of energy
If a charge-pump power supply is used to dynamically adjust voltage based on signal levels, then power consumption is reduced, but device complexity increases
Solution Approach 1:
The charge-pump circuit serves as an intermediary between the battery power source and the power amplifier. This intermediate stage enables dynamic voltage adjustment without requiring complex modifications to the main amplifier circuitry. The charge-pump acts as a buffer that translates constant battery voltage into variable amplifier supply voltage, simplifying the overall system architecture while achieving power savings.
Data Source
AI summary
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 control circuit controls a power supply that supplies the power supply rails to the power amplified output stage. The voltage of the power supply rails 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.