Class-G Audio Amplifier Buck Control for Low-Power, Low-Distortion Output
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Solution Overview
Problem
Conventional class-AB audio amplifiers have high power consumption due to their inefficiencies, especially during light loads, and suffer from crossover distortion and electromagnetic interference, while class-D amplifiers are more efficient but use expensive components and have a worse EMI profile.
Innovation Solution
An audio amplifier with an embedded buck controller operating in a class-G configuration, which includes a buck converter that adjusts output voltage based on detected peak amplitudes and introduces a delay in the signal processing chain to ensure settling time, reducing power consumption and preventing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional class-AB amplifiers are used, then audio quality is maintained, but power consumption is high especially during light loads
Solution Approach 1:
The amplifier dynamically switches between class-AB and class-D operating modes based on the instantaneous amplitude of the audio signal. During light loads, it operates in class-AB mode to maintain audio quality, and during heavy loads, it switches to class-D mode to reduce power consumption. This dynamic operation resolves the contradiction between maintaining audio quality and reducing power consumption across different operating conditions.
Solution Approach 2:
The amplifier changes its operating parameters (bias currents, supply voltage levels) based on the signal amplitude detected by the envelope detector. By adjusting these parameters dynamically, the amplifier achieves low power consumption during light loads while maintaining high audio quality during heavy loads, resolving the contradiction between power efficiency and audio performance.
2Use of energy by moving object
If class-D amplifiers are used, then power consumption is reduced, but EMI increases and components become more expensive
Solution Approach 1:
The amplifier dynamically selects between class-AB and class-D modes based on signal conditions. During light loads where class-D operation would generate excessive EMI, the system operates in class-AB mode which produces lower EMI. During heavy loads where power efficiency is critical, it switches to class-D mode. This dynamic selection resolves the contradiction between power consumption and EMI generation.
3Speed
If output voltage is changed quickly to follow audio signal, then responsiveness is improved, but voltage settling time causes distortion
Solution Approach 1:
The envelope detector continuously monitors the audio signal amplitude in advance and triggers voltage level changes before they are needed. This preliminary detection allows the amplifier to prepare for upcoming signal demands, switching supply voltages proactively rather than reactively, thereby reducing distortion caused by settling time while maintaining fast responsiveness.
Solution Approach 2:
The system uses feedback from the envelope detector to continuously monitor signal amplitude and adjust the supply voltage accordingly. This feedback mechanism ensures that voltage changes are made at the optimal moment, balancing the need for fast response with the requirement for adequate settling time, thus resolving the contradiction between speed and settling accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces power consumption by up to 50% during light loads and maintains audio quality by ensuring sufficient headroom and settling time, while minimizing electromagnetic interference.
Implementation Method 1
a buck controller having a supply input configured to receive a battery voltage, the buck controller configured to control an output voltage at the first supply terminal
Implementation Method 2
a delay insertion circuit configured to receive a processed digital stream from the digital signal processing circuit and configured to provide the processed digital stream to the class-AB driver stage a delay time after receiving the processed digital stream, where the delay time is based on the settling time
Implementation Method 3
an audio amplitude detector having an input coupled to the input of the first audio bridge and configured to detect a first peak amplitude in the first digital audio stream
Data Source
AI summary
An audio amplifier includes: a buck controller configured to control an output voltage at a first supply terminal, the output voltage selected from a set including a plurality of output voltages, where the output voltage takes a settling time to settle; a first audio bridge including: a class-AB driver stage coupled to the first supply terminal, and a delay insertion circuit configured to receive a processed digital stream and provide the processed digital stream to the class-AB driver stage a delay time after receiving the processed digital stream, where the delay time is based on the settling time; and an audio amplitude detector configured to detect a first peak amplitude in the first digital audio stream, where the buck controller is configured to select a lowest output voltage from the set that is higher than the first peak amplitude plus a headroom voltage.