Class-D Amplifier Feedback Loops for Pop and Click Suppression
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Solution Overview
Problem
Class-D amplifiers are susceptible to artifact noise such as pop and click noise during power up and power down due to sudden changes in DC offset voltage and PWM pulses, which limits their adoption in mobile devices despite their high efficiency and dynamic range.
Innovation Solution
The implementation of a Class-D amplifier with a primary and auxiliary feedback loop system, where the programmable gain of the power driver is minimized at power up and maximized at power down, and vice versa, to divert undesired transients away from the speaker, using a controller module to smoothly ramp gains and hand off signals between the loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Class-D amplifier suddenly applies DC offset voltage and PWM pulses to speaker terminals during power up, then amplifier can quickly start operation, but artifact noise such as pop and click noise is generated
Solution Approach 1:
The patent applies preliminary action by pre-charging the output capacitor through a switch before connecting to the speaker terminals. This preliminary charging action ensures that when the amplifier transitions to normal operation, there is no sudden voltage step applied to the speaker, thereby preventing pop and click noise while maintaining fast startup performance.
2Speed
If Class-D amplifier suddenly removes DC offset voltage and PWM pulses from speaker terminals during power down, then amplifier can quickly stop operation, but artifact noise such as pop and click noise is generated
Solution Approach 1:
The patent applies preliminary action during power down by gradually reducing the PWM duty cycle to zero before completely disconnecting from the speaker terminals. This preliminary reduction action allows the output voltage to smoothly transition to zero, preventing sudden voltage changes that would cause pop and click noise while maintaining fast power down capability.
3Device complexity
If Class-D amplifier uses traditional feedback loop, then circuit is simple, but transient pulses during power transitions cause pop and click noise
Solution Approach 1:
The patent applies segmentation by dividing the feedback loop into two distinct paths: a main feedback loop for normal operation and an auxiliary feedback loop specifically for transient suppression during power transitions. This segmentation allows the auxiliary loop to handle transient conditions separately, preventing pop and click noise while maintaining the simplicity of the main feedback path.
Data Source
AI summary
A Class-D amplifier arrangement is disclosed that implements an auxiliary feedback loop and a primary feedback loop. The auxiliary feedback loop operates upon an input signal when the Class-D amplifier arrangement is operating under a power-up condition and a power-down condition so that a modulated signal is confined within the auxiliary feedback loop during the power-up condition and the power-down condition. The confinement of the modulated signal within the auxiliary feedback loop during the power-up condition and the power-down condition diverts transient signals coupled onto the modulated signal from an output device. The primary feedback loop operates upon the input signal when the Class-D amplifier arrangement is operating under a normal condition so that the modulated signal is introduced to the output device during the normal condition.