Single-Bit Audio Amplifier Feedback for Noise Reduction
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Solution Overview
Problem
Conventional audio processing technologies for noise reduction in devices like portable Bluetooth earphones often compromise on area and power consumption, and dynamic range enhancement affects the signal's dynamic headroom.
Innovation Solution
An audio processing apparatus and method utilizing a digital processing circuit to generate an N-bit digital audio signal, which is truncated and modulated using pulse width or pulse density modulation to produce a single-bit waveform, and an amplifier circuit with a single-bit DAC and closed-loop feedback to reduce noise while maintaining low power consumption and small area requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional noise reduction technologies are used, then noise is reduced, but area and power consumption increase
Solution Approach 1:
The patent changes the bit depth parameter from multi-bit to single-bit representation, transforming the audio signal format to enable noise reduction through quantization noise shaping while maintaining low power consumption. The single-bit sigma-delta modulation approach fundamentally alters the signal parameters to achieve noise reduction without requiring complex high-power processing circuits
Solution Approach 2:
The patent replaces complex analog noise reduction circuits with a digital signal processing approach using single-bit sigma-delta modulation. This substitution of mechanical/analog systems with digital signal processing enables noise reduction functionality while consuming minimal power, as the noise filtering is achieved through digital modulation rather than analog circuitry
2Object-affected harmful factors
If conventional noise reduction technologies are used, then noise is reduced, but device area increases
Solution Approach 1:
The patent changes the signal representation parameter from multi-bit to single-bit, which dramatically reduces the complexity of the required processing circuits. This parameter change enables noise reduction functionality to be implemented with minimal circuit area, as single-bit sigma-delta modulation requires only simple modulators and demodulators rather than complex multi-bit processing circuits
Solution Approach 2:
The patent extracts and separates the noise reduction functionality into a dedicated single-bit modulation stage, isolating the noise shaping process from the main audio processing path. This extraction allows noise reduction to be achieved through a dedicated simple module rather than requiring complex integrated noise reduction circuits that would occupy significant device area
3Object-affected harmful factors
If dynamic range enhancement is used to reduce noise, then noise is reduced, but dynamic headroom of the signal is affected
Solution Approach 1:
The patent implements a feedback mechanism in the single-bit sigma-delta modulation system where the quantized single-bit signal is fed back through the modulator. This feedback loop shapes the quantization noise to higher frequencies while maintaining the dynamic headroom of the original signal, achieving noise reduction without compromising the signal's dynamic range characteristics
Solution Approach 2:
The patent uses periodic oversampling in the single-bit modulation process, where the audio signal is sampled at a rate much higher than the Nyquist rate. This periodic high-rate sampling distributes quantization noise across a wider frequency spectrum, allowing noise reduction in the audible range while preserving dynamic headroom through the periodic nature of the oversampling process
Data Source
AI summary
The present disclosure discloses an audio processing apparatus having noise reducing mechanism. A DSP circuit generates N-bit digital audio signal, N being an integer larger than 1. A first modulation circuit truncates the digital audio signal and performs a first modulation processing based on pulse width or pulse density modulation to generate a single-bit waveform modulated signal. An amplifier includes a single-bit DAC circuit, a second modulation circuit and a driving circuit. The single-bit DAC circuit converts the single-bit waveform modulated signal to generate an input analog signal. The second modulation circuit subtracts the input analog signal and an output modulated signal to generate a subtraction result and performs a second modulation processing thereon to generate a control signal. The driving circuit generates the output modulation signal according to the control signal and transmits the output modulation signal to the second modulation circuit through a closed-loop feedback path.