Class D Audio Amplifier Feedback for Low-Noise PWM Signals
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Solution Overview
Problem
Conventional Class D audio amplifiers face noise interference issues due to analog audio inputs, which degrade output signal quality, and existing solutions that mitigate this often require costly components like complex PWM modulators and high-speed A/D converters.
Innovation Solution
A system using a simple linear PWM modulator to convert digital audio signals to PWM format, eliminating the need for feedback loops and high-speed A/D converters, with a Class D audio amplifier incorporating feedback loops to minimize noise interference and improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a high resolution/high speed D/A converter and closed-loop Class D audio amplifier are used, then output signal quality with very low distortion is achieved, but noise interference degrades the quality of the output signal
Solution Approach 1:
The patent extracts the audio signal processing from the analog domain and performs it entirely in the digital domain. The digital audio signal is directly fed to the PWM modulator and Class D amplifier, bypassing the D/A converter and analog audio input stages that introduce noise. This extraction of the signal path from the noisy analog domain resolves the contradiction between achieving high output signal quality and avoiding noise interference.
2Object-affected harmful factors
If a complex PWM modulator and high speed A/D converter are used to avoid noise, then noise interference is minimized, but device complexity and cost increase
Solution Approach 1:
The patent replaces expensive, complex components (complex PWM modulator and high-speed A/D converter) with simpler, more economical components. By keeping the audio signal in digital format throughout processing and using a simple linear PWM modulator with an open-loop Class D amplifier, the system achieves noise-free operation without requiring costly high-speed A/D conversion or complex modulation circuits.
Solution Approach 2:
Instead of converting digital audio to analog and then back to digital (as in the conventional method with A/D converter), the patent inverts the approach by maintaining the signal in digital format throughout the entire processing chain. The digital audio signal is directly modulated by a simple linear PWM modulator and amplified by the Class D amplifier, eliminating the need for A/D conversion entirely.
3Manufacturing precision
If additional filters are added between the output stage and the audio speaker, then the filtered signal quality is improved, but device complexity increases
Solution Approach 1:
The patent eliminates the need for additional filtering by maintaining continuous digital signal processing throughout the system. The digital audio signal remains in digital format through the PWM modulator and Class D amplifier, avoiding the analog domain where filtering would be required. This continuous digital processing approach achieves high signal quality without adding complex filter stages.
Data Source
AI summary
The present invention introduces methods and systems to amplify digital audio signals for driving speakers. First, digital audio signals are converted to PWM audio signals by a liner PWM modulator that is open-loop. Then, PWM audio signals are amplified by a Class D audio amplifier that has at least one feedback loop.