Digital Amplifier PWM Reset Control to Prevent Pop Noise
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Solution Overview
Problem
Existing digital amplifiers generate noise when resetting, requiring complex structures with additional circuits to stop audio output without noise, which is inefficient and prone to pop noise.
Innovation Solution
Adjusting the gain of the digital audio signal to zero and superposing a predetermined dither, then generating a pulse-width modulated signal to control switching elements, allowing for a simple configuration to stop audio output without noise by shifting from a sound-generating to an anacoustic state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the gate voltage application to MOS-FET is stopped to perform reset operation, then the speaker is forcedly stopped and ceases to generate sound, but noise and pop noise are generated during the transition
Solution Approach 1:
Before stopping the MOS-FET switching operation, the duty ratio of the PWM signal is gradually adjusted from its current value to 50% over a predetermined period. This preliminary adjustment ensures that both MOS-FETs are in the same state before shutdown, preventing noise generation during the reset transition.
Solution Approach 2:
The reset process dynamically adjusts the duty ratio over time rather than abruptly changing it. The control unit continuously modifies the PWM signal duty ratio during the reset period, creating a smooth transition that eliminates pop noise while maintaining the reset function.
2Object-generated harmful factors
If additional circuits are added to stop audio output without noise, then noise during resetting is reduced, but the device structure becomes complex
Solution Approach 1:
The control unit that normally controls PWM signal generation is also used to control the reset process. By making the control unit multi-functional, the patent eliminates the need for separate reset control circuits while still achieving noise-free audio output stopping during reset operations.
Solution Approach 2:
The reset control function is merged with the existing PWM signal control function. The control unit integrates both the normal audio signal generation and the reset operation control, eliminating redundant circuits and simplifying the overall device structure while maintaining noise-free reset capability.
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; a synchronizing section operable to synchronize the pulse-width modulated signal with a reset signal that resets the digital audio signal; and a control section operable to perform a resetting operation by setting the gain of the digital audio signal to a zero level upon receiving the reset signal, stopping the superposing of the dither to thereby generate the pulse-width modulated signal, and setting the pulse-width modulated signal to the “low” state by using the pulse-width modulated signal synchronized with the reset signal, thereby causing the switching element to stop performing the switching operation.