Class D Amplifier Ramp Control for Click-Pop-Free State Transitions
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Solution Overview
Problem
Class D amplifiers in audio systems experience undesirable transient signals, such as 'click/pop' noise, when transitioning between operation states, leading to audible artifacts and potential damage to electrical components.
Innovation Solution
A closed-loop amplifier system with a modulator that uses a pulse-width modulated (PWM) output signal and a ramp generator to adjust the closed-loop transfer function during state transitions, smoothing the transition between activated and deactivated states by varying the gain and phase margin of the system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the class D amplifier transitions between operation states, then the system can change between activated and deactivated states, but transient signals such as click/pop noise occur causing audible artifacts
Solution Approach 1:
The system applies preliminary action by pre-charging or pre-discharging the output capacitor before transitioning between operation states. This preliminary charging/discharging action prepares the output voltage to match the target state, preventing abrupt voltage changes that would cause transient signals and audible artifacts during state transitions.
Solution Approach 2:
The system changes parameters by dynamically adjusting the charging/discharging current of the output capacitor during state transitions. By controlling the current parameter and transition timing, the system smoothly transitions between activated and deactivated states without generating harmful transient signals, thus resolving the contradiction between transition capability and transient signal generation.
2Speed
If the amplifier transitions quickly between states, then the response time is improved, but transient artifacts such as click/pop noise increase
Solution Approach 1:
The system performs preliminary charging or discharging of the output capacitor before the actual state transition occurs. This preliminary action pre-adjusts the output voltage to the target level, enabling the amplifier to switch states rapidly without generating audible artifacts, thus achieving both fast transition speed and clean output.
Solution Approach 2:
The system introduces an intermediary transition phase where the output capacitor is charged or discharged through controlled current paths before the main state switch occurs. This intermediary action mediates between the fast switching requirement and the artifact-free output requirement, allowing rapid transitions without direct abrupt voltage changes that would cause click/pop noise.
Data Source
AI summary
A closed loop amplifier system comprising a modulator that provides a pulse-width modulated (PWM) output signal based on an input signal, the modulator having a variable closed loop transfer function. The system also comprises a ramp generator that provides a ramp signal to the modulator, the variable closed loop transfer function of the modulator varying as a function of the ramp signal. The system further comprises a controller that controls the ramp generator to provide the ramp signal to adjust the variable closed loop transfer function during transitions between operating states of the amplifier system.