1 Introduction

At the output stage of the class-D amplifier of power-on or power-off, the noise is generated by a voltage difference before it stays its steady state. Usually without proper circuit design or power sequence control, the system event related to the analog amplifier generates a click or a pop. For Class D amplifier of the audio portion, audible click sound, mainly depending on the both amplifier and the amplifier, is typically at PWM start and stop.

System design considers the pop sound at the system level at the beginning to avoid the pop noise. The power up and the power down is, in most occasions, the pop noise occurred. The power up and power down impacts the DC offset of amplifier input, which results in the voltage transient change. This short time voltage transient outputs and applies on the speaker to generate the undesired sound. If the audio input source change also has the possibility to get the voltage transient change, then the amplifier outputs the pop noise. For more details on how to define and measure the pop noise, see the Click and Pop Measurement Technique.

Impedance mismatching on the input components will also dramatically impact the DC offset that mainly dominates the pop noise occasions on the system design.

Pop and click, which can be observed through the portable speaker or headphone when you power on or off the power supply, are the appellation given to the popping noise. Pop and click, especially true for those destined for the SE input circuit, is a characteristic that makes a lot of impact in the world of audio amplifiers. This application report indicates the methods on how to eliminate the pop noise with minimal audio low frequency attenuation impact on woofer application.