PWM Audio Signal Interleaving to Reduce RF Interference
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Solution Overview
Problem
Conventional digital audio systems experience interference with RF signals due to the energy spectrum of PWM signals, particularly because altering the center frequency is difficult, leading to significant interference with AM radio signals.
Innovation Solution
A method and system for interleaving a digital audio signal by generating a second PWM signal with a reduced carrier frequency, extracting specific frames from both the first and second PWM signals, and interleaving them to create a third PWM signal that reduces the peak of the energy spectrum, thereby minimizing interference with RF signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the carrier frequency of PWM signal is maintained at high value (e.g., 768 kHz), then the digital audio signal can be transmitted effectively, but the energy spectrum causes interference with RF signals such as AM radio
Solution Approach 1:
The patent divides the original high-frequency PWM signal into multiple lower-frequency PWM signals by extracting and interleaving frames at different time points. This segmentation approach maintains the total energy required for effective audio transmission while distributing the energy spectrum across multiple lower frequency components, thereby reducing peak interference with RF signals
Solution Approach 2:
The patent employs periodic frame extraction and interleaving at specific time intervals to generate the divided PWM signals. By periodically sampling and interleaving frames from the original signal, the system maintains signal integrity while transforming the energy spectrum distribution to reduce RF interference
2Object-generated harmful factors
If the center frequency of energy spectrum is changed to reduce RF interference, then interference with RF signals decreases, but the implementation is not facile given that energy spectrum appears at every multiple of carrier frequency
Solution Approach 1:
Instead of changing the carrier frequency, the patent changes the temporal distribution parameters of the PWM signal by dividing it into multiple lower-frequency signals through frame extraction and interleaving. This parameter transformation approach achieves spectrum redistribution and RF interference reduction without the complexity of frequency adjustment
3Object-generated harmful factors
If the peak of energy spectrum is lowered to minimize RF interference, then interference with RF signals is reduced, but the total energy for effective audio transmission must be maintained
Solution Approach 1:
The patent merges multiple lower-frequency PWM signals through frame interleaving to reconstruct the audio signal. This merging process distributes the total energy across multiple frequency components, lowering the peak energy spectrum while maintaining the cumulative energy required for effective audio transmission
Data Source
AI summary
A system, a method for interleaving a digital audio signal including a PWM signal, and a digital audio processing device employing the same in accordance with the present invention are disclosed. The system, the method and the digital audio processing device is capable of minimizing the interference with an RF signal such as an AM signal or an FM signal by interleaving the digital audio signal including the PWM signal.