Class-D Amplifier Pre-Charging to Eliminate Pop-Click Noise
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Solution Overview
Problem
Conventional class-D amplifiers often produce severe pop-click noise due to sudden current surges in audio applications, particularly affecting earphones and EarPods, which is a critical issue in audio systems.
Innovation Solution
A class-D amplifier design incorporating a loop filter, control signal generator, first and second power drivers, and pre-charging circuit to pre-charge output terminals to a common voltage, suppressing voltage drops and enabling a settling circuit to eliminate pop-click noise by disabling the second loop when the first loop is enabled.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PWM control is used to achieve high efficiency, then power losses are significantly reduced, but pop-click noise is generated due to sudden current surges
Solution Approach 1:
The patent applies preliminary action by pre-charging the output terminals to a common voltage level before the main power driver is enabled. The pre-charging circuit charges both the positive and negative output terminals to the same voltage, ensuring that no voltage difference exists between them at startup. This preliminary charging action prevents sudden current surges when the main amplifier is activated, thereby eliminating pop-click noise while maintaining the high efficiency benefits of PWM control
2Device complexity
If the amplifier is enabled directly without pre-charging, then the circuit is simple, but voltage drops occur causing pop-click noise
Solution Approach 1:
The patent introduces an intermediary pre-charging circuit that acts as a mediator between the power supply and the main power driver. This pre-charging circuit includes switching elements and capacitors that temporarily charge the output terminals before the main amplifier is activated. The intermediary circuit adds minimal complexity while effectively preventing voltage drops and pop-click noise, representing a practical compromise between simplicity and noise elimination
3Stability of the object's composition
If the second loop is enabled for settling, then the loop filter and control signal generator are settled, but the second loop must be disabled when the first loop is enabled
Solution Approach 1:
The patent applies dynamics by implementing a dynamic switching mechanism between the second settling loop and the first main loop. The control system automatically enables the second loop during the settling phase to stabilize the loop filter and control signal generator, then seamlessly switches to the first loop when the main amplifier is activated. This dynamic approach ensures stability during different operational phases while managing loop control complexity through automated switching
Data Source
AI summary
A class-D amplifier with low pop-click noise is shown. A loop filter, a control signal generator, a first power driver, and a first feedback circuit are provided within the class-D amplifier to establish a first loop for signal amplification. The class-D amplifier further has a settling circuit and a pre-charging circuit. The settling circuit is configured to be combined with the loop filer and the control signal generator to establish a second loop to settle the loop filter and the control signal generator before the first loop is enabled. The pre-charging circuit is configured to pre-charge a positive output terminal and a negative output terminal of the first power driver.