Class H Amplifier Supply Tracking for Low-Interference Audio Output
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Solution Overview
Problem
Conventional class AB amplifiers for driving headphones and loudspeakers are inefficient, with high power consumption due to excessive supply current, and existing high-efficiency amplifier solutions for loudspeakers often cause interference with discontinuous switching modes.
Innovation Solution
A Class H amplifier design with an autonomous Class H supply that uses a Buck converter with switches of varying sizes and a feedback loop to minimize switching losses, allowing for efficient power delivery with low output impedance, and a charge pump with feedback to stabilize voltage rails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a class AB amplifier is used to drive headphones, then the amplifier can deliver sufficient output power, but the power consumption is high due to excessive supply current
Solution Approach 1:
The amplifier dynamically adjusts the supply voltage to match the instantaneous signal requirements. The voltage rails are continuously variable and track the signal swing, allowing the amplifier to operate at minimum necessary voltage levels rather than maintaining a fixed high supply voltage, thereby reducing power consumption while maintaining output power capability
Solution Approach 2:
The supply voltage parameter is changed from a fixed value to a continuously variable value that adapts to the signal amplitude. This parameter change enables the amplifier to operate efficiently across different signal levels by adjusting the voltage rails in real-time, reducing unnecessary power dissipation
2Use of energy by moving object
If separately controlled DC-DC converters and charge pumps are used to increase efficiency, then power efficiency improves, but interference occurs due to discontinuous switching modes
Solution Approach 1:
The amplifier maintains continuous operation of the voltage rail generation circuitry, avoiding discontinuous switching modes. The charge pump and voltage rails operate continuously rather than being switched on and off, which eliminates the interference and noise associated with discontinuous operation while maintaining high efficiency
Solution Approach 2:
The amplifier employs feedback control to regulate the voltage rails continuously. The feedback mechanism ensures stable operation of the charge pump and voltage generation circuitry, preventing the discontinuous modes that cause interference while maintaining optimal efficiency through active regulation
3Use of energy by moving object
If the supply voltage is lowered to match the signal swing for maximum efficiency, then efficiency increases, but the amplifier lacks headroom for proper operation
Solution Approach 1:
The voltage rails are made dynamic and continuously adjustable, allowing the amplifier to maintain just enough headroom above the signal swing at any given moment. This dynamic adjustment ensures maximum efficiency while providing sufficient operating margin, unlike fixed voltage designs that must accommodate peak signals throughout the entire signal range
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 achieves high efficiency comparable to Class D amplifiers while maintaining performance levels of Class AB amplifiers, reducing power consumption and minimizing interference, with the ability to generate double the DC voltage for enhanced output.
Implementation Method 1
The voltage rail generation circuit includes a Buck converter with switches of different size to reduce switching losses
Implementation Method 2
a charge pump with feedback to stabilize voltage rails
Data Source
AI summary
A class H amplifier circuit includes a Buck converter 20 and a charge pump 30 which are used to generate voltages which are used in turn to power an output driver 10. A feedback path 36 controls the loop. The circuit is particularly suitable as a high efficiency circuit for driving headphones or loudspeakers.