Abstract: Modern smart phones and tablet computers typically incorporate multiple wireless services at different frequency bands ranging from FM radio to LTE. At the same time, an increasing number of designs utilize more than one antenna to enhance sensitivity and suppress cross-talk. Both trends place the miniature RF solid-state switches in an increasingly crucial role in smart mobile device RF front end designs. This paper will give an overview of both high and low throw-count RF switches used in different circuit locations in a typical mobile device design, and discuss how each performance specification and design feature will impact on the overall performance of your system. In addition, this paper will dive deeper inside each RF switch module and reveal current and future trends in core RF switching technologies.
Introduction
Global enthusiasm for data-centric smart mobile devices exploded when several leading cell-phone makers pioneered in integrating multiple wireless communication technologies into one small box that is “always connected” to the Internet. Since then, users of smart phones, tablet computers, and e-readers all crave faster data-rates and more functionality, which has pushed the entire industry on both ends: on one end, better wireless standards/technologies, such as evolved high-speed packet access (HSPA+) and long term evolution (LTE), are being developed and adapted by big service carriers; and on the other end, more wireless services, such as GPS, mobile TV, and RFID, are being integrated into each smart mobile device. Both trends translate into the same impact on RF front end design of these devices: more frequency bands and better signal quality (Figure 1). In the near future, a smart mobile device can easily operate in 12 or more cellular bands, plus WiFi, WiMAX, GPS, Bluetooth®, mobile FM/TV, RFID, and other non-cellular services. With such large amounts of parallel chains to be integrated, RF front end engineers face great challenges in coping with exploded RF component counts and power consumption, while maintaining signal quality over a wide frequency range across bands.