Class-D PWM Amplifier Gain Switching for Idle Noise Reduction
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Solution Overview
Problem
Class-D pulse width modulation amplifiers face challenges in minimizing idle channel noise due to the inability to clamp their outputs to ground voltage without causing audio artifacts, as the inputs toggle at a 50% duty cycle, making it difficult to reduce noise effectively.
Innovation Solution
A system with a forward signal path and feedback signal path that operates in two modes: one with higher forward gain and lower feedback gain when signal content is present, and another with lower forward gain and higher feedback gain when signal content is absent, allowing for reduced noise by adjusting impedances and quantizer gain to minimize idle channel noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the output of a class-D amplifier is clamped to ground voltage to reduce idle channel noise, then idle channel noise is reduced, but audio artifacts are introduced that are perceptible to listeners
Solution Approach 1:
The patent applies dynamics by making the amplifier operate in two distinct modes: a first mode during signal presence and a second mode during idle channels. The control subsystem dynamically switches between these modes based on signal detection, allowing the amplifier to optimize performance for each condition. This resolves the contradiction by enabling noise reduction during idle channels without introducing artifacts during signal playback.
Solution Approach 2:
The patent changes operating parameters by adjusting the duty cycle of the pulse width modulation during idle channels. Specifically, the modulated signal is adjusted to have a duty cycle that reduces idle channel noise while maintaining proper operation. This parameter change allows the system to reduce noise without the need for output clamping that would cause audio artifacts.
2Object-affected harmful factors
If the driver loop of the class-D amplifier is placed into an open circuit to enable output clamping, then idle channel noise is reduced, but the amplifier cannot maintain proper operation during signal content
Solution Approach 1:
The control subsystem dynamically switches the driver loop configuration between connected and open circuit states based on signal presence. During signal content, the driver loop remains connected for proper operation. During idle channels, the driver loop is placed in an open circuit to enable output clamping and noise reduction. This dynamic switching resolves the contradiction between noise reduction and reliable operation.
Solution Approach 2:
The system performs preliminary detection of signal content presence before switching modes. The control subsystem detects whether signal content is present and proactively switches the amplifier to the appropriate mode beforehand, ensuring that the driver loop is in the open circuit state before idle channel noise becomes an issue, and reconnects before signal content arrives to maintain proper operation.
3Measurement precision
If the forward gain is increased to maintain open loop amplifier gain during mode switching, then signal fidelity is maintained, but idle channel noise increases
Solution Approach 1:
The patent applies dynamics by switching between different forward gain values based on operating mode. During signal presence (first mode), a first forward gain is used to maintain signal fidelity. During idle channels (second mode), a second forward gain is used that is optimized for noise reduction. The control subsystem dynamically adjusts the forward gain based on signal detection, resolving the contradiction between signal fidelity and noise reduction.
4Stability of the object's composition
If the feedback gain is decreased to maintain loop dynamics during mode switching, then stability is maintained, but noise reduction effectiveness is reduced
Solution Approach 1:
The control subsystem dynamically adjusts feedback gain based on operating mode. During signal presence, a first feedback gain is used to maintain loop dynamics and stability. During idle channels, a second feedback gain is applied that is optimized for noise reduction while maintaining adequate loop stability. This dynamic adjustment resolves the contradiction between stability and noise reduction effectiveness.
Data Source
AI summary
A system may include a forward signal path having a forward gain and configured to receive an input signal at an input and generate an output signal at an output as a function of the input signal, a feedback signal path having a feedback gain and coupled between the output and the input, and a control subsystem configured to operate the forward signal path and the feedback signal path in at least two modes comprising a first mode in which the forward gain is a first forward gain and the feedback gain is a first feedback gain and a second mode in which the forward gain is a second forward gain smaller than the first forward gain and the feedback gain is a second feedback gain larger than the first feedback gain. The control subsystem may cause operation in the first mode when signal content is present in the input signal and may cause operation in the second mode when signal content is absent from the input signal.