Audio Signal Filtering for Class-D Power Supply Pumping Prevention
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Solution Overview
Problem
Existing class-D amplifiers experience power supply voltage fluctuations due to the power supply pumping phenomenon, where the voltage fluctuates as a result of regenerative current overcharging the smoothing capacitors, and existing solutions only start controlling this fluctuation after the phenomenon occurs, not preventing it.
Innovation Solution
An audio processing device that includes a signal processing circuit capable of selecting between two frequency-reduced signals, one with a first frequency and one with a higher second frequency, and a processor that determines the intensity of the low-frequency component in the audio signal to control the circuit to switch between these states, thereby reducing the power supply voltage fluctuation before it occurs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the cutoff frequency of the high-pass filter is increased stepwise to reduce power supply voltage fluctuation, then the power supply voltage stability is improved, but the control response is delayed because the fluctuation must be detected first
Solution Approach 1:
The patent applies preliminary action by proactively increasing the cutoff frequency of the high-pass filter when low-frequency components are detected in the audio signal, before power supply voltage fluctuation actually occurs. This prevents the power supply pumping phenomenon from happening in the first place, rather than reacting after detection of voltage instability.
Solution Approach 2:
The patent implements feedback by continuously monitoring the audio signal for low-frequency components and dynamically adjusting the cutoff frequency of the high-pass filter accordingly. When low-frequency components exceed a threshold, the system increases the cutoff frequency to prevent power supply voltage fluctuation, creating a closed-loop control system.
2Stability of the object's composition
If the cutoff frequency of the high-pass filter is increased to prevent power supply pumping phenomenon, then the power supply voltage stability is improved, but the audio signal quality may deteriorate due to loss of low-frequency components
Solution Approach 1:
The patent applies dynamics by making the cutoff frequency of the high-pass filter variable rather than fixed. The cutoff frequency is dynamically adjusted based on the presence and intensity of low-frequency components in the audio signal, allowing the system to optimize between power supply stability and audio quality in real-time.
Solution Approach 2:
The patent changes the parameter of cutoff frequency dynamically based on signal conditions. When low-frequency components are present, the cutoff frequency is increased to prevent power supply pumping; when they are absent, the cutoff frequency is reduced to preserve audio quality, thus adapting the system parameters to operating conditions.
Data Source
AI summary
An audio processing device includes: a signal processing circuit configured to select between a first state for outputting a first signal obtained by reducing components that fall below a first frequency in an audio signal and a second state for outputting a second signal obtained by reducing components that fall below a second frequency in the audio signal, and output one of the selected first or second signal as an output signal, where the second frequency is higher than the first frequency; a class-D amplifier that amplifies the output signal; a processor configured to: determine whether or not an intensity of a low-frequency component in the audio signal exceeds a threshold value; and control the signal processing circuit to select: the first state in a case where a determination result is negative, where the intensity of the low-frequency component in the audio signal is determined to not exceed the threshold value; and the second state in a case where the determination result is affirmative, where the intensity of the low-frequency component in the audio signal is determined to exceed the threshold value.