Section 5: Source-measure concepts
Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
5-8
4200A-SMU-900-01 Rev. A December 2020
Remote sensing
The remote sensing method shown in the following figure is generally preferred for measurements on
low-impedance DUTs. With this configuration, the test current I is forced through the DUT through
one set of test cables, while the voltage across the DUT is measured through a second set of sense
cables. Although some small current (I
S
) may flow through these sense cables, it is usually negligible
(typically pA or less) and can generally be ignored. Since the voltage drop across the sense cables is
negligible, the voltage actually measured by the SMU (V
M
) is essentially the same as the voltage
across the DUT (V
DUT
).
Figure 76: Remote sensing
Source or sink
Depending on how they are programmed and what is connected to the output (load or source), the
SMUs can operate in any of the four quadrant of operation, as shown in the following figures. When
operating in the first (I) or third (III) quadrant, the SMUs are operating as a source (voltage and
current have the same polarity). As a source, the SMUs are delivering power to a load.
When operating in the second (II) or fourth (IV) quadrant, the SMUs are operating as a sink (voltage
and current have opposite polarity). As a sink, they dissipate power rather than sourcing it. An
external source (such as another SMU) or an energy storage device (such as a capacitor) can force
operation into the sink region.
