Class D amplifiers are becoming more widely used due to their superior efficiency over Class AB amplifiers. According to market research firm Gartner, the compound annual growth rate of Class D amplifiers between 2006 and 2011 will reach 15.6%, from $334 million to $688 million. The main growth driver comes from power consumption sensitivity and space. Restricted consumer electronics. However, the topology of the Class D amplifier switching output brings high frequency EMI. How to control the EMI of the Class D amplifier is an aspect that system engineers must consider. Generation of EMI in Class D amplifiers Varying voltage and current signals generate electromagnetic field radiation that creates electromagnetic interference (EMI: Electro-MagneTIc Interference), which affects the normal operation of products such as radios, televisions, and cell phones. In order to prevent EMI problems in electronic equipment, countries around the world have established relevant standards, such as the Federal Communications Commission (FCC: Federal CommunicaTIon Commission) certification, the purpose is to limit the electromagnetic radiation of electronic products. The EMI test is performed in a specific anechoic chamber to measure the intensity of the electromagnetic wave radiated from the product and must not exceed the specified maximum energy compared to specifications such as the FCC. In the FCC specification, products are classified into CLASS A and CLASS B according to their purposes. Class A is for commercial or industrial use, Class B is for household use, and FCC has stricter regulations for Class B products. Figure 1: CLASS A and CLASS B standards for the FCC specification The topology of the traditional Class D amplifier switching output is a good source of EMI emissions: such as modulated switching signals, edge changes in switching signals, and varying current signals on the power line, which generate a large amount of EMI, as shown in the following figure. Figure 2: Topology of the Class D Amplifier Switch Output Bluetooth speaker,Portable bluetooth speaker, wireless protable outdoor speaker SHENZHEN YINZHIGUAN DIGITAL TECHNOLOGY CO.,LTD , http://www.yzgmusiccrown.com
