Digital Amplifier PWM Muting to Prevent Pop Noise and Radiation
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Solution Overview
Problem
Conventional digital amplifier muting methods generate unnecessary radiation and noise due to abrupt changes in PWM outputs during the muting process, leading to discontinuous audio output and potential pop noise.
Innovation Solution
The gain of the digital audio signal is adjusted to an anacoustic level, and a predetermined dither is added, with the pulse-width modulated signal's high and low states gradually shortened to maintain the signal in the low state, effectively stopping the switching operation and preventing noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PWM outputs are abruptly set to the same phase and 50% duty ratio to achieve muting, then the speaker stops generating sound, but unnecessary radiation and noise are generated due to switching strains
Solution Approach 1:
The patent applies preliminary action by gradually transitioning the PWM duty ratios to 50% before final muting. The control unit incrementally adjusts the duty ratios over multiple cycles rather than abruptly setting them, which prevents switching strains and noise while achieving the muting function.
Solution Approach 2:
The patent uses dynamics by making the PWM duty ratios changeable over time rather than fixed. The control unit dynamically adjusts the duty ratios from their initial values to 50% in incremental steps, allowing the system to transition smoothly from audio output to muting state without generating harmful radiation or noise.
2Reliability
If the transistors continue switching during muting operation, then the muting function is maintained, but switching strains cause unnecessary radiation
Solution Approach 1:
The patent applies preliminary action by first adjusting the duty ratios to 50% while continuing switching, then subsequently stopping the switching operation. This preliminary adjustment ensures that when switching stops, no potential differences are generated, thus preventing radiation while maintaining the muting function.
Solution Approach 2:
The patent uses beforehand cushioning by ensuring that the duty ratios are equalized to 50% before stopping the switching operation. This preparatory step cushions against the potential generation of radiation by eliminating potential differences before the switching cessation that would otherwise cause abrupt changes.
3Object-generated harmful factors
If the PWM outputs are forcedly set to low state to prevent noise, then radiation is reduced, but audio output becomes discontinuous
Solution Approach 1:
The patent applies preliminary action by first equalizing the duty ratios to 50% before forcing the PWM outputs to the low state. This preliminary equalization ensures that no potential differences exist, so when the outputs are forced to low, audio continuity is maintained while noise and radiation are prevented.
Solution Approach 2:
The patent uses beforehand cushioning by equalizing duty ratios prior to forcing the low state, cushioning against discontinuities in audio output. This ensures smooth transition while maintaining audio continuity and preventing noise generation.
Data Source
AI summary
A digital amplifier apparatus includes a gain-adjusting section operable to adjust a gain of a digital audio signal; a dither-superposing section operable to superpose a predetermined dither on the digital audio signal; a pulse-width-modulated signal generating section operable to generate a pulse-width-modulated signal corresponding to the digital audio signal; an amplifying section operable to cause a switching element to perform a switching operation in accordance with the pulse-width-modulated signal; a pulse-width changing section operable to change a ratio between a “high” state and a “low” state of the pulse-width modulated signal; and a control section operable to perform a muting process by causing the gain-adjusting section to set the gain of the digital audio signal to a zero level, the dither-superposing section to stop superposing the dither, and the pulse-width changing section to change, step by step, the ratio between the “high” state and the “low” state of the pulse-width modulated signal toward the “low” state upon receipt of a predetermined muting signal for muting the digital audio signal, thereby maintaining the “low” state and stopping the switching operation performed in accordance with the pulse-width modulated signal.