Self-Oscillating Class D Amplifier Filtering Beat Noise
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Solution Overview
Problem
Self-excited class D amplifier circuits generate beat noise due to frequency differences, which can be exacerbated by variable load impedance, leading to distorted audio signals and decreased sound quality when attempting to synchronize oscillations with a high-level synchronizing signal.
Innovation Solution
Incorporating a band elimination filter in the amplifying device to reduce components within the frequency band of the synchronizing signal, thereby stabilizing the self-oscillation frequency and minimizing beat noise, even with fluctuating load impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-level synchronizing signal is supplied to synchronize self-oscillation, then the difference between self-oscillation frequency and synchronizing signal frequency is reduced, but distortion is generated in the audio signal waveform and sound quality is degraded
Solution Approach 1:
A band elimination filter is introduced as an intermediary component between the class D amplifier circuit and the output. This filter selectively removes the synchronizing signal frequency components from the output without affecting the audio signal, thereby allowing the use of higher-level synchronizing signals for better synchronization while eliminating the harmful frequency components that would otherwise cause distortion
Solution Approach 2:
The harmful frequency components corresponding to the synchronizing signal frequency are extracted and removed from the output signal using the band elimination filter. This allows the synchronizing signal to maintain sufficient amplitude for reliable synchronization while its unwanted frequency components are separated and eliminated
2Adaptability or versatility
If the impedance of the load connected to the class D amplifier circuit is variable, then the amount of delay in the negative feedback channel fluctuates, but this causes the self-oscillation frequency to fluctuate and increases the difference from the synchronizing signal frequency
Solution Approach 1:
The band elimination filter provides a feedback mechanism by continuously monitoring and removing frequency components at the synchronizing signal frequency from the output. This feedback loop compensates for frequency fluctuations caused by variable load impedance, maintaining stable synchronization by actively correcting deviations from the target frequency
Solution Approach 2:
The band elimination filter acts as an intermediary that decouples the output from the harmful effects of frequency fluctuations. By removing the problematic frequency components regardless of their source, it allows the system to adapt to variable load conditions while maintaining stable oscillation frequency through the synchronizing signal
3Productivity
If multiple self-excited class D amplifier circuits are juxtaposed in an audio system, then the system functionality is enhanced, but beat noise is generated due to differences in oscillation frequencies among the circuits
Solution Approach 1:
The band elimination filter provides a universal solution that can be applied to each class D amplifier circuit in a multi-circuit system. By uniformly removing the synchronizing signal frequency components from each circuit's output, it enables multiple circuits to operate simultaneously without generating beat noise, thereby maintaining system functionality while eliminating the harmful interference
Solution Approach 2:
The presence of multiple amplifier circuits, which initially causes beat noise due to frequency differences, is converted into a benefit through the band elimination filter. The filter removes the problematic frequency components, allowing the multiple circuits to be used for enhanced functionality (such as multi-channel audio or higher power output) while the harmful beat noise is eliminated
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses beat noise and maintains sound quality by synchronizing self-oscillations with a synchronizing signal of lower levels, reducing distortion and harmonic distortion, while ensuring the oscillation frequency remains stable despite load impedance variations.
Implementation Method 1
a band elimination filter, in which, the modulation circuit is configured to receive, from a signal generation circuit, a supply of a synchronizing signal with which the self-oscillation synchronizes; and in which, the band elimination filter is configured to reduce components that belong to a frequency band including a frequency of the synchronizing signal
Data Source
AI summary
An amplifying device includes a self-excited class D amplifier circuit and a band elimination filter. The self-excited class D amplifier circuit includes a modulation circuit that is configured to apply self-oscillating pulse modulation to an audio signal. The modulation circuit is configured to receive, from a signal generation circuit, a supply of a synchronizing signal with which the self-oscillation synchronizes. The band elimination filter is configured to reduce components that belong to a frequency band including a frequency of the synchronizing signal, in an output signal from the self-excited class D amplifier circuit.