The market size of mobile phones continues to expand every year. Particularly, the number of multifunctional mobile phones called smart phones equipped with high performance processors has been growing remarkably more than conventional mobile phones.
Generally, smart phones have built-in wireless communication functions, such as 2G/3G, wireless LAN and Bluetooth®. We believe that these smart phones will successively respond to the next generation high-speed communications standards including LTE (Long Term Evolution) in the future.
Smart phones will become even more user friendly mobile phones along with the high functionalization. On the other hand, there are problems currently occurring, such as noise coupled from the baseband circuit, due to the built-in multiple wireless communication functions, and the design changes to solve the reception sensitivity deterioration caused by this noise coupling, takes a lot of time and manpower for the mobile phone manufacturers to solve these problems.
As a detailed example, there are many cases where the noise from the baseband portion of the mobile phone radiates from the FPC (flexible printed circuit board) connected to the main board, and the audio signal line can be mentioned as a typical usage location of an FPC. In the case of smart phones, they are generally connected to a speaker via an FPC or etc. from the main board. There are many cases where this FPC becomes the antenna which emits noise radio waves and causes problems.
As one solution for such a problem, it is becoming clear that the use of chip inductors for the chokes is effective. This paper introduces the inductors (LQW15Cseries/LQW18C series) which can also be used for the audio signal line, particularly the speaker line.