Class-H Amplifier Supply Tracking for High-Volume Audio Efficiency
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Solution Overview
Problem
Class-D amplifiers in portable communication devices face efficiency degradation when boosting voltage to achieve higher speaker volume, as the combination of boost circuits and class-D amplifiers loses efficiency at higher power levels, especially when spending less time in bypass mode.
Innovation Solution
A circuit with a voltage boost mechanism that provides a variable supply voltage continuously proportional to the audio input signal, allowing the boost circuit to follow the output of the class-D amplifier, transitioning between bypass and boost modes based on audio signal thresholds to maintain efficiency across a wide range of power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a boost circuit is used to raise supply voltage above 5V for higher speaker volume, then the speaker output volume is improved, but the efficiency of the boost circuit and class-D amplifier combination degrades at higher power levels
Solution Approach 1:
The supply voltage to the class-D amplifier is made dynamic rather than fixed. The boost circuit continuously adjusts the supply voltage level based on the instantaneous demand, transitioning between bypass mode (at lower power levels) and boost mode (at higher power levels). This dynamic adaptation allows the system to maintain high efficiency at low power while providing sufficient voltage headroom at high power levels.
Solution Approach 2:
The supply voltage parameter is changed from a fixed value to a variable parameter that continuously tracks the audio signal envelope. By monitoring the audio input signal and adjusting the supply voltage accordingly, the system optimizes the operating point of the class-D amplifier to maintain high efficiency across different output power levels while preventing clipping and distortion.
2Reliability
If the boost circuit operates continuously at higher voltage to maintain headroom, then the amplifier can handle peak signals without clipping, but the efficiency degrades even at lower power levels where bypass mode would be sufficient
Solution Approach 1:
The boost circuit operates in a periodic or near-periodic manner, activating only when the audio signal envelope indicates high power demand. The circuit continuously monitors the audio signal and switches between bypass and boost modes based on instantaneous requirements, ensuring that the high-voltage operation occurs only when necessary to maintain signal integrity and prevent clipping.
Solution Approach 2:
The system automatically adjusts its own supply voltage based on the audio signal characteristics without external intervention. The envelope detector and control circuitry continuously monitor the audio input and self-regulate the boost circuit operation, transitioning between modes to maintain optimal efficiency and signal integrity automatically.
Data Source
AI summary
An amplifier circuit includes an amplifier and a voltage boost circuit configured to provide a variable supply voltage to the amplifier, the variable supply voltage continuously proportional to an audio input signal, the variable supply voltage configured to follow an output of the amplifier.