Source measure unit

The Keithley 236 introduced in 1989 was the first stand-alone SMU and allowed system builders to integrate one or more SMUs with a separate PC control.

Over time stand-alone SMUs have evolved to offer a broader range of current, voltage, power level and price points for applications beyond semiconductor characterization.

Bench power supplies might add constant-current operation as well as providing limited measurement capabilities, but these are in many cases still one-quadrant only and with margins of errors acceptable for coarse lab-work.

Some high-end lab power-supplies will have two- or four-quadrant operation (source and sink, with fixed or dual polarity), which is an essential feature of a SMU.

These may have advanced capabilities of controlling the power output, but might lack things like specialized test-modes or monitoring-options tailored for precise and easy power-characterization.