Differential Class D Audio Amplifier With Active Feedback
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Solution Overview
Problem
Class AB amplifiers exhibit low efficiency, leading to increased power dissipation, heat management issues, and reduced battery life in audio applications, necessitating the development of more efficient power amplifiers.
Innovation Solution
A fully differential class D audio power amplifier with active feedback, employing a pulse width modulation circuit and rail-to-rail comparators, and a supply-independent reference voltage circuit to minimize power dissipation and enhance harmonic distortion reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If class AB amplifiers are used to drive speaker load, then audio quality is maintained, but power efficiency deteriorates and heat dissipation increases
Solution Approach 1:
The patent changes the operating parameters of the amplifier by switching from class AB continuous conduction mode to class D switching mode, where power transistors operate in fully on or fully off states. This parameter change fundamentally alters the power efficiency characteristic while maintaining audio quality through PWM modulation and active feedback
Solution Approach 2:
The patent implements active feedback by feeding back a portion of the output signal to the input stage. This feedback mechanism corrects harmonic distortion and maintains audio quality despite the aggressive switching operation, resolving the contradiction between efficiency and audio fidelity
2Temperature
If class AB amplifiers are used, then audio output is achieved, but heat management complexity increases due to heat sink requirements
Solution Approach 1:
The patent extracts and eliminates the heat sink component from the system by adopting class D architecture. The switching operation minimizes power dissipation in the output stage, removing the need for external heat dissipation components and simplifying the overall device structure
Solution Approach 2:
By changing the conduction mode parameter from continuous (class AB) to switching (class D), the patent fundamentally reduces the thermal load generated during operation, eliminating the need for complex heat management structures
3Use of energy by moving object
If class AB amplifiers are used, then audio performance is maintained, but battery life decreases due to high power consumption
Solution Approach 1:
The patent changes the power consumption parameter by implementing class D switching architecture where power transistors operate in low-dissipation states (fully on or fully off). This parameter change directly extends battery life by reducing overall power consumption while maintaining audio output performance
Solution Approach 2:
The patent employs periodic PWM switching action to deliver audio power efficiently. The high-frequency switching allows energy to be transferred in controlled pulses, minimizing wasted energy and maximizing battery efficiency compared to continuous class AB operation
4Loss of energy
If class D amplifiers use switching transistors, then power efficiency improves, but thermal runaway risk is partially mitigated
Solution Approach 1:
The patent implements active feedback that continuously monitors and corrects output signals. This feedback mechanism compensates for the partial thermal runaway mitigation, ensuring stable operation and maintaining audio quality by correcting any distortion introduced by the switching operation
Data Source
AI summary
A fully differential class D amplifier is provided. The class D amplifier includes an active amplifier in the feedback path of the modulator. In one embodiment, the class D amplifier includes a fully differential amplifier as an input buffer, in which a supply-independent reference voltage is used as the common mode voltage of the output of the fully differential amplifier. In one embodiment, the class D amplifier includes a pulse width modulation circuit that includes rail-to-rail comparators.