- A sourcemeter is an electronic instrument capable of generating currents and voltages and simultaneously measuring them with high accuracy.
- A sourcemeter is also called a Source Measure Unit or SMU.
- A SMU combines a precision direct current (DC) power supply, a power source, a digital multimeter and an electronic load in the same unit. It can also incorporate a pulse generator. All these functions integrated in the same housing are closely synchronized.
This instrument can force a voltage or a current to a given value and simultaneously perform accurate voltage and/or current measurements.
A sourcemeter is used for precision demanding applications such as the current-voltage (I-V) characterization of silicon carbide (SiC) and gallium nitride (GaN) semiconductor circuits, batteries, photovoltaic cells, LEDs, DC-DC converters, power MOSFET circuits, lighting systems, and other non-linear components.
Four quadrant operation
A four-quadrant sourcemeter can deliver and receive energy. It can therefore generate or absorb current whatever the voltage, positive or negative. It can operate in source mode or in active load mode automatically on 4 quadrants.
As shown in the figure above, a typical power supply can only supply voltage or current. In other words, it can only operate in two quadrants (in quadrants I and III), but a sourcemeter (SMU) can operate in four quadrants because it is capable of both supplying and dissipating energy, acting both as a power source and as an electronic load. By operating as a source or sink, it can simultaneously measure voltage, current and resistance.
- Keithley Instruments, acquired by Tektronix in late 2010, is one of the leading specialists in this type of instrument. Its 2400 series SMU feature a five-inch touch screen. They can simultaneously supply and measure a current of 10 fA at 10 A in pulse mode and/or a voltage of 100 nV at 1100 V (for a maximum power of 1000 W in pulse mode and 100 W in DC mode). These instruments measure DC voltages with an accuracy of up to 0.012% with a resolution of 6.5 digits.
- On February 16, 2021, Rohde & Schwarz entered the market for source and measurement units with the launch of the R&S NGU201 two-quadrant and R&S NGU401 four-quadrant source meters. These sourcemeters cover six current ranges from 10 µA (with a resolution of 100 pA) to 10 A (with a resolution of 10 µA). They offer an accuracy of up to 0.025% over all current ranges. Voltage is measured with a resolution of 10 µV in the 20 V range and 1 µV in the 6 V range.
- There are also sourcemeters integrated in PXI format boards such as the GX3104 module offered by Marvin Test Solutions. The GX3104 is a 3U PXI format module capable of simultaneously forcing and sensing voltage and current over a range of ±20 V and up to ±1 A (channel 1) while channels 2 to 4 can each deliver currents up to 500 mA. The module can provide a total output current of 1A. All four channels are electrically isolated from the PXI power supply and share an isolated common ground.
