Eva Murphy and Padraig Fitzgerald
Analog Devices

The universal serial bus (USB) has become a dominant interface to fulfill the ever increasing needs for rapid data transfer between end devices—for example, downloading and uploading data between PCs and portable devices such as cell phones, digital cameras, and personal media players.

CMOS switches can be used for connecting and routing data lines in USB systems. By selecting suitable switches, designers can significantly shorten design cycles by enhancing existing designs rather than developing new ones. In this article, we describe the USB, then go on to explore the crucial role of switches in improving performance in applications such as portable media players, cell phones, and wireless pen drives. We also show how key parameters of the switches affect the overall system design and discuss basic design challenges, such as the trade-offs between meeting bandwidth requirements and minimizing signal reflections. Additionally, we suggest how to maximize the opening in eye diagrams by careful board layout.