Adaptive PWM Feedback Circuit for Low-Noise Audio Signal Processing
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Solution Overview
Problem
Conventional digital pulse-width modulation methods increase noise floor in audio signal processing systems, leading to noticeable background noise when audio signals are small, due to high total harmonic distortion plus noise (THD+N).
Innovation Solution
A signal processor and method that utilize a mixer, pulse-width modulator, power stage circuit, and feedback circuit to generate a mixed signal, modulate it, amplify, and selectively provide feedback to suppress harmonics and noise, switching between different feedback paths based on signal scale to minimize THD+N.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If conventional digital pulse-width modulation method is used to process audio signal, then the harmonics are suppressed, but the noise floor is increased leading to obvious background noise
Solution Approach 1:
The patent implements dynamic switching between two different feedback paths based on the input signal level. When the input signal is large, the first feedback path (from power stage output) is activated to suppress harmonics. When the input signal is small, the second feedback path (from PWM output) is activated to avoid noise amplification. This dynamic adaptation resolves the contradiction between harmonics suppression and noise floor control.
Solution Approach 2:
The patent changes the feedback signal source parameter based on input signal characteristics. By switching the feedback origin between the power stage output and PWM output, the system adapts its noise and harmonic suppression characteristics to match the input signal level, thereby resolving the trade-off between harmonics suppression and noise floor elevation.
2Manufacturing precision
If feedback circuit is used to suppress harmonics, then total harmonic distortion is reduced, but background noise becomes more obvious for small audio signals
Solution Approach 1:
The patent segments the feedback path into two distinct routes: the first feedback path sampling from the power stage output for large signal harmonics suppression, and the second feedback path sampling from the PWM output for small signal noise avoidance. This segmentation allows selective application of feedback based on signal level, resolving the contradiction between THD reduction and background noise control.
Solution Approach 2:
The patent employs dual feedback paths with different sampling points. The first feedback path provides harmonics suppression for large signals, while the second feedback path prevents noise amplification for small signals. By selectively activating appropriate feedback paths, the system achieves both low THD and low background noise across different operating conditions.
Data Source
AI summary
A signal processer is configured to decrease total harmonic distortion plus noise of an output signal generated from an input signal. The signal processer includes a mixer, a pulse-width modulator, a power stage circuit, and a feedback circuit. The mixer is configured to mix the input signal and a feedback signal to generate a mixed signal. The pulse-width modulator is configured to module the mixed signal to generate a modulated signal and output the modulated signal from an output terminal of the pulse-width modulator. The power stage circuit is configured to amplify the modulated signal to generate the output signal and output the output signal from an output terminal of the power stage circuit. The feedback circuit is configured to generate a feedback signal selectively according to the modulated signal or the output signal.