Hybrid Class AD Audio Amplifier for Low-Distortion Output
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Solution Overview
Problem
Class D audio amplifiers offer high efficiency but suffer from distortion and output ripple, while linear amplifiers provide high fidelity but low efficiency, lacking a solution that balances both factors effectively.
Innovation Solution
A hybrid Class AD audio amplifier is introduced, combining a Class D amplifier with a linear output stage biased by floating power supplies, which converts pulse width modulated signals into analog audio signals with reduced distortion and improved fidelity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a Class D amplifier is used, then efficiency is improved, but distortion and output ripple increase
Solution Approach 1:
The amplifier is divided into two distinct stages: a Class D switching amplifier stage for high efficiency power amplification, and a separate linear output stage for signal refinement. This segmentation allows each stage to optimize its function - the Class D stage handles the bulk power conversion efficiently while the linear stage cleans up distortion and ripple, resolving the contradiction between efficiency and signal quality.
Solution Approach 2:
A linear output stage is introduced as an intermediary between the Class D switching stage and the load. This intermediary linear stage processes the already-amplified signal from the Class D stage, reducing distortion and output ripple without significantly impacting the overall efficiency achieved by the Class D architecture.
2Object-generated harmful factors
If a linear amplifier is used, then fidelity is improved, but efficiency deteriorates
Solution Approach 1:
Instead of using a full linear amplifier for the entire amplification task, only a partial linear output stage is employed to perform the specific function of reducing distortion and ripple. The majority of the amplification work is done by the efficient Class D stage, so the linear stage operates partially to provide the necessary signal refinement without the excessive energy consumption of a complete linear amplifier.
3Power
If Class D amplifier operates at high power, then output power is improved, but distortion increases
Solution Approach 1:
The amplification function is segmented between the Class D switching stage which provides high power output, and a separate linear output stage which specifically addresses distortion. This allows the system to deliver high output power through the Class D stage while the linear stage simultaneously reduces the distortion that inevitably increases at high power levels.
Data Source
AI summary
An audio amplifier comprising a Class D audio amplifier having an input receiving an analog input signal, a pulse width modulation stage for converting the analog input signal to a pulse width modulated signal, a driver stage receiving the pulse width modulated signal and for producing a driver PWM signal and an output switching audio amplifier stage receiving the driver PWM signal and providing an amplified PWM signal; an output filter stage receiving the amplified PWM signal for converting the amplified PWM signal into an analog audio signal; and a linear output amplifier stage receiving as inputs the analog input signal and the output of the output filter stage, the output of the output filter stage serving to bias the linear output amplifier stage. In one embodiment, two floating power supplies are superimposed on the output of the filter stage for biasing the linear amplifier, one at a preset voltage above the output signal of the filter stage and a second at a preset voltage below the output of the filter stage. The linear output amplifier stage provides an analog output to a sound reproduction transducer.