Digital Input Class-D Amplifier With Analog Feedback for Low Noise
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Solution Overview
Problem
Conventional audio amplifiers with digital input signals face challenges in reducing noise levels, particularly for digital input audio signals, as they require high power consumption and sophisticated digital-to-analog converters, making them costly and impractical for modern applications with stringent noise requirements.
Innovation Solution
A digital input class D amplifier is designed with a DAC modulator that converts digital input signals into a quasi-digital signal, which is then processed by a class D modulator with an analog feedback loop, eliminating the need for a digital feedback loop and reducing noise levels by using only a single amplification stage and eliminating the DAC reconstruction filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional audio amplifier uses a DAC followed by an amplifier to process digital input signals, then the digital signal can be converted and amplified, but the noise level increases and power consumption rises
Solution Approach 1:
The patent combines the DAC and amplifier into a single integrated class-D amplifier circuit that processes digital signals directly. The class-D amplifier architecture integrates the digital-to-analog conversion and power amplification functions in one stage, eliminating the need for separate DAC and reconstruction filter components. This merging reduces the number of noise-generating stages while maintaining efficient power operation.
Solution Approach 2:
The patent replaces the traditional analog reconstruction filter with a digital filtering approach implemented in the class-D amplifier's modulation circuitry. By using pulse-width modulation (PWM) with digital signal processing, the system achieves low-pass filtering functionality without requiring a separate analog filter stage, thereby reducing noise and component count while maintaining power efficiency.
2Measurement precision
If a conventional audio amplifier uses two amplifier circuits (DAC amplifier and output amplifier), then the signal can be processed, but the noise level increases
Solution Approach 1:
The patent merges the DAC amplifier and output amplifier into a single class-D amplifier stage. The class-D architecture uses a single amplification stage that directly drives the speaker through PWM switching, eliminating the need for a separate DAC reconstruction filter and its associated amplifier. This single-stage design reduces noise accumulation while simplifying the overall circuit architecture.
Solution Approach 2:
The patent extracts and eliminates the redundant DAC reconstruction filter and its amplifier from the signal path. By using direct digital-to-analog conversion within the class-D amplifier followed by PWM modulation, the system removes the intermediate analog filtering stage that would otherwise require a separate amplifier, thereby reducing noise and device complexity.
3Measurement precision
If a sophisticated DAC is used to reduce noise, then noise level decreases, but cost and power consumption increase
Solution Approach 1:
The patent replaces the need for a sophisticated, expensive DAC with a simpler class-D amplifier architecture that processes digital signals directly using PWM modulation. The digital signal processing and modulation circuits in the class-D amplifier provide adequate digital-to-analog conversion functionality without requiring high-precision DAC components, thereby reducing cost while maintaining acceptable noise performance.
Solution Approach 2:
The patent changes the operating parameters of the amplifier system by using high-frequency PWM switching in the class-D architecture. This approach allows the system to achieve low noise performance through modulation techniques rather than through high-precision DAC components, enabling cost-effective implementation with reduced noise levels through parameter optimization rather than component sophistication.
Data Source
AI summary
An audio amplifier receiving a digital input audio signal and generating an output audio signal for driving a speaker includes a digital input class D amplifier configured to receive the digital input audio signal and to generate the output audio signal. The digital input class D amplifier includes a first modulator configured to receive the digital input audio signal and to generate a quasi-digital signal in n-bit, and a class D modulator configured to receive the n-bit quasi-digital signal and to generate the output audio signal, the class D modulator implementing an analog feedback loop. In some embodiments, the class D modulator is implemented using a PWM modulator. In other embodiments, the PWM modulator incorporates enhanced features to improve the output noise characteristics.