Class D Audio PWM Circuit With Non-Synchronized Channel Switching
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Solution Overview
Problem
Class D power amplifiers used in audio devices, especially multichannel stereos, suffer from electromagnetic interference (EMI) due to simultaneous switching of multiple channels, which worsens the EMI problem at signal edges.
Innovation Solution
An audio signal modulation and amplification circuit comprising a common-mode electric potential controller, a carrier signal generator, and multiple channel circuits, where the common-mode electric potential controller generates distinct common-mode electric potentials, and the carrier signal generator produces carrier signals based on these potentials to generate pulse-width modulation (PWM) signals that drive the channel circuits, ensuring non-synchronized switching and reduced EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If digital power amplification technology is used in class D amplifiers, then amplification efficiency is improved, but electromagnetic interference (EMI) is generated at signal edges
Solution Approach 1:
The patent uses pulse-width modulation (PWM) to convert the audio signal into periodic pulse trains. The switching elements operate in periodic on/off states, achieving efficient digital power amplification while the periodic nature allows for controlled EMI characteristics through frequency selection and synchronization strategies.
Solution Approach 2:
The patent introduces an modulator as an intermediary component that processes the audio signal before it reaches the power switching stage. This modulator converts the audio signal into PWM format, acting as a buffer that separates the low-power signal processing from the high-power switching operations, thereby reducing direct EMI coupling.
2Reliability
If multiple channels are switched simultaneously in multichannel stereos, then channel synchronization is improved, but electromagnetic interference problem is worsened
Solution Approach 1:
The patent employs periodic PWM switching for each channel with carefully selected frequencies and phases. By using periodic action with different duty cycles and timing for each channel, the system maintains functional synchronization while avoiding simultaneous switching of multiple channels, thereby reducing cumulative EMI effects.
Solution Approach 2:
The patent introduces asymmetry in the switching timing and duty cycles of different channels. Each channel operates with unique PWM parameters, preventing symmetric simultaneous switching that would maximize EMI. This asymmetric approach maintains channel independence and reduces constructive interference while preserving audio synchronization.
Data Source
AI summary
An audio signal modulation and amplification circuit includes a common-mode electric potential controller, a carrier generator, and channel circuits. The common-mode electric potential controller is configured to generate one or more first common-mode electric potentials and second common-mode electric potentials. The carrier generator is adapted to receive the first common-mode electric potential to generate a carrier signal. Each of the channel circuits includes a filter, a comparison circuit, and a driving circuit. The filter is adapted to filter an input signal and generate a filtered signal based on a corresponding one of the second common-mode electric potentials. The comparison circuit is configured to compare the potential of the carrier signal with the potential of the filtered signal to generate a pulse-width modulation signal. The driving circuit is configured to be turned on or off in response to the pulse-width modulation signal to output a load driving signal.