Class D Amplifier Soft Mute Transition for Pop Noise Suppression
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Solution Overview
Problem
Class D amplifiers generate audible pop noises due to offset and mismatching in the feedback loop, especially during transient events such as sudden changes in audio signals, which are uncomfortable for listeners.
Innovation Solution
A circuit design that includes an integrating amplifier, a voltage regulator, and a control module to manage the transition between mute and un-mute modes by gradually enabling or disabling the amplifier and regulator, respectively, to minimize offset and noise during mode changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If class D amplifier operates with sudden start or finish of large audio signal, then audio performance is achieved, but pop noise is generated causing listener discomfort
Solution Approach 1:
The patent applies preliminary action by gradually enabling the integrating amplifier circuit before full operation begins. The control module responds to mode switch signal changes by progressively activating the amplifier and simultaneously deactivating the voltage regulator, allowing the output to transition smoothly from regulated voltage to integrated analog signal without sudden jumps that cause pop noise
Solution Approach 2:
The patent implements dynamics by making the amplifier and regulator transition gradually rather than abruptly. The control module dynamically adjusts the operating states of both circuits in response to mode switch signals, creating a smooth temporal progression that eliminates sudden output changes and associated pop noise while maintaining audio performance
2Power
If offset in output stage is larger than 20 mV, then amplification function is performed, but audible pop noise is produced at transient events
Solution Approach 1:
The patent uses the control module as an intermediary that coordinates the transition between voltage regulator and integrating amplifier circuits. This intermediary control ensures that the amplifier is gradually enabled while the regulator is simultaneously disabled, preventing sudden offset changes from causing audible pop noise while preserving the amplification capability
3Productivity
If integrating amplifier circuit is suddenly enabled, then audio signal processing begins, but output node experiences sudden change causing pop noise
Solution Approach 1:
The control module performs preliminary action by gradually enabling the integrating amplifier circuit in response to mode switch signal changes. This gradual activation allows the output node to transition smoothly from the voltage regulator's output to the amplifier's integrated signal, preventing sudden changes that would generate pop noise while still enabling efficient signal processing
Data Source
AI summary
A class D amplifier receives and amplifies a differential analog signal which is then differentially integrated. Two pulse width modulators generate pulse signals corresponding to the differentially integrated analog signal and two power units generate output pulse signals. The outputs the power units are coupled to input terminals of integrators via a resistor feedback network. An analog output unit converts the pulse signals to an output analog signal. The differential integration circuitry implements a soft transition between mute/un-mute. In mute, the integrator output is fixed. During the soft transition, the PWM outputs change slowly from a fixed 50% duty cycle to a final value to ensure that no pop noise is present in the output as a result of mode change.