Frequency modulation (FM) receivers have been used in high-definition music and voice broadcasting for many years. It can provide excellent sound quality, signal stability and noise resistance. Recently, FM receivers have begun to appear in more mobile and personal media players and other market applications. For battery life, the combination of class D amplifiers is an inevitable trend in the selection of post-stage power amplifiers; but its most important The problem is EMI interference.
The solution to the interference of FM in the workshop is shielded by a metal shell to attenuate the interference energy of harmonic radiation, thereby making FM reception normal. However, when the FM receiver is combined with a Class D amplifier, this shielding method is not applicable, and it is necessary to start with the EMI prevention of the Class D amplifier.
Figure 1 shows the received signal at the antenna end of a general FM receiver. When the Class D power amplifier is operating, if the harmonic signal radiated by it is ineffective, the result will be as shown in Figure 2. The harmonic signal overwrites the original FM signal, which reduces the quality of the FM reception and even makes it impossible to receive.
The problem of EMI interference can be approached from both radiation and conduction. The choice of PCB layout and LC filter to block radiation interference is an effective processing direction. According to the frequency band radiated by the Class D amplifier, adjusting the combination of the output LC filter can effectively improve the FM reception quality. As shown in Figure 3: The interference phenomenon of the original Figure 2 can be eliminated by the appropriate LC filter to eliminate the interference problem of the Class D amplifier.
Conducted emission via power / ground is another source of interference. In addition to the isolation on the PCB Layout, a coupling filter is the appropriate choice.
The use of external components to deal with the interference problems of FM receivers can indeed have a certain effect. However, the problems of higher cost and appearance size are not conducive to the promotion of products. The fundamental solution is still to be handled within the IC. Existing Class D amplifiers generally only consider the pure EMI radiation specifications. The interference problem of system integration is not well understood, so it has always been an interference source on the system. Class D power amplifier is more convenient for system integration and application will be the subject of relevant suppliers.
Screen Printing Machine,Screen Printing Equipment,Screen Press Machine,Automatic Screen Printing Machine
Zhijiang BSL battery technology service company , https://www.bslbatteryservice.com