Class-D Amplifier Pre-Charging to Eliminate Pop-Click Noise
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Solution Overview
Problem
Conventional class-D amplifiers suffer from severe pop-click noise, particularly when powering on, due to sudden current surges into the load, which is a critical issue in audio systems like earphones and EarPods.
Innovation Solution
A class-D amplifier design incorporating a loop filter, control signal generator, first power driver, first feedback circuit, settling circuit, and pre-charging circuit to establish multiple loops for signal amplification and pre-charging the output terminals to a common voltage, thereby eliminating the pop-click noise by suppressing voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If PWM control is used to reduce power losses in the output stage, then amplifier efficiency is improved, but pop-click noise is generated due to sudden current surges into the load
Solution Approach 1:
The patent applies preliminary action by pre-charging the output terminals to the input voltage level before the main power switch is turned on. This is achieved through a pre-charging circuit that connects the output terminals to the input voltage source via a pre-charging switch during a pre-charge period, eliminating the voltage difference that would otherwise cause sudden current surges and pop-click noise when the amplifier is enabled.
2Device complexity
If the amplifier is enabled directly without pre-charging, then device complexity is reduced, but severe pop-click noise occurs at power-on
Solution Approach 1:
The patent implements preliminary action by introducing a pre-charging circuit with a pre-charging switch that activates before the main power switch. This circuit pre-charges the output terminals to match the input voltage level, preventing sudden current surges. The pre-charging switch is controlled by a pre-charge enable signal that is activated during a predetermined pre-charge period, ensuring smooth power-on without pop-click noise while maintaining relatively simple circuit architecture.
Data Source
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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.