The personal computer (PC), currently the standard information- processing device for office and home use, communicates with most peripherals using the universal serial bus (USB). Standardization, cost, and the availability of software and development tools have made the PC very attractive as a host-processor platform for medical and industrial applications, but the safety and reliability requirements of these growing markets—especially regarding electrical isolation—are very different from the office environment that has historically driven the design of the personal computer.

In the early days, personal computers were provided with serial and parallel ports as standard interfaces to the outside world. These legacy standards had been inherited from the earliest mainframe computers. Another available communication standard, RS-232, though slow, fit well into medical and industrial environments because it allowed easy implementation of the required robust isolation. Its low speed and point-to-point nature were tolerated because it was universally available and well supported.

USB, which has come to replace RS-232 as a standard port in personal computers and their peripherals, has features that are far superior to the older serial port in nearly every respect. It has been difficult and costly to provide the necessary isolation for medical and industrial applications, however, so USB has been principally used for diagnostic ports and temporary connections.

This article discusses various ways of applying isolation with USB. In particular, a new option, the ADuM41601 USB isolator, is now available from Analog Devices. This breakthrough product allows simple, inexpensive isolation of peripheral devices—especially including the D+ and D– lines—increasing the usefulness of USB in medical and industrial applications.