Model 4200A-SCS Source-Measure Unit (SMU) User's Manual
Section 5: Source-measure concepts
4200A-SMU-900-01 Rev. A December 2020
5-5
In the following figure, the driven GUARD is connected to the metal guard plate for the insulators.
Since the voltage on either end of R
L1
is the same (0 V drop), no current can flow through the leakage
resistance path. As a result, the SMU or preamplifier measures only the current through the DUT.
Figure 72: Test fixture - guarded
The guard signal has an output impedance of 100 kΩ, which is effective only when connected to
high-impedance loads.
Local and remote sensing
The type of sensing, local or remote, is automatically selected depending on the connections.
Local sensing is adequate for many test and measurement situations. However, you should use
remote sensing for maximum accuracy for the following source-measure conditions:
•
Test circuit impedance <1 kΩ
•
Maximum voltage source or voltage measurement accuracy are required
Specified accuracies for both source and measure are achieved using remote sensing.
