In high-speed RF ATE, signal generators—which determine the core speed of performance—are often the weakest link with respect to test time. To improve this speed, engineers use step attenuators external to the signal generator to reduce the need for the signal generator to change power settings. A step attenuator makes it possible to produce a broad range of output power levels from a single source without changing the power setting. This improves seek time and repeatability of the source characteristics across a wide power range. Step attenuators have used mechanical-switching systems for years, but these switches tend to wear out and they have bounce problems. In the past, solid-state solutions have proven impractical because of speed limitations. Profound, yet simple advances in multichip-module technology using GaAs FET switches and LEDs in a common surface-mounted package have made it possible to create a more useful step attenuator for ATE applications. This technology uses light from small, high-intensity LEDs to significantly enhance the FET switch's performance. An FET switch has many advantages over its mechanical equivalent, and designers have long sought after it as a solution in ATE systems.