Class-D PWM Frequency Offsetting for Stereo SNR Improvement
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Solution Overview
Problem
Audio systems using class-D amplifiers face degradation in signal-to-noise ratio (SNR) due to interference between stereo audio channels, particularly in the 20 Hz to 200 kHz audio band, leading to adverse harmonic frequency components.
Innovation Solution
An audio system employing a first and second pulse width modulation (PWM) signal generation unit, each with feedback, integration, low-pass filtering, phase delaying, and switching units, generates switching signals with a frequency difference greater than 20 kHz to minimize interference effects, thereby removing harmonic frequency components from the audio band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If class-D amplifiers are used for high efficiency, then energy efficiency is improved, but signal to noise ratio is degraded due to interference between stereo channels
Solution Approach 1:
The patent applies asymmetry by intentionally creating a frequency difference between the first and second switching signals. The second switching signal is designed to have a different frequency than the first switching signal, which asymmetrically positions the harmonic frequency components of each channel at different frequencies. This prevents the harmonic components from overlapping and interfering with each other in the audio band, thereby improving signal to noise ratio while maintaining class-D amplifier efficiency.
2Adaptability or versatility
If stereo audio channels are processed independently, then channel independence is maintained, but interference between channels occurs in the audio band
Solution Approach 1:
The patent resolves channel interference by transitioning from the time domain to the frequency domain. Instead of processing stereo channels independently at the same frequency, the invention introduces a frequency dimension difference between the two channels. The first and second switching signals operate at different frequencies, which separates their spectral content and prevents interference in the audible audio band while maintaining independent channel processing.
3Device complexity
If switching signals are generated at the same frequency, then system simplicity is maintained, but harmonic frequency components cause adverse interference
Solution Approach 1:
The patent applies parameter changes by modifying the frequency parameter of the switching signals. Specifically, the second switching signal is generated with a different frequency than the first switching signal. This parameter change ensures that the harmonic frequency components of each channel appear at different frequencies, preventing their overlap and interference in the audio band, while maintaining relatively simple system architecture.
Data Source
AI summary
An audio system performing a class-D amplification includes a first pulse width modulation (PWM) signal generation unit and a second PWM signal generation unit. The first PWM signal generation unit generates a first switching signal based on a first audio signal. The second PWM signal generation unit generates a second switching signal based on a second audio signal. The second switching signal has a frequency difference with respect to the first switching signal such that a harmonic frequency component generated by interference between the first switching signal and the second switching signal is removed. Accordingly, the audio system performing the class-D amplification may improve a signal to noise ratio by minimizing influence of the harmonic frequency components on the first and second switching signals.