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In this section:
Source-measure concepts ....................................................... 5-1
Guarding .................................................................................. 5-1
Local and remote sensing ........................................................ 5-5
Source or sink .......................................................................... 5-8
Source-measure considerations ............................................. 5-12
Sweep concepts ..................................................................... 5-19
Operation mode timing ........................................................... 5-22
Source-measure concepts
•
(on page 5-1): An overview of guarding, guarding concepts, guard connections, and
test fixture guarding.
•
(on page 5-5): Describes sensing, sensing concepts, and sense
selection.
•
(on page 5-8): Describes source and sink operations and summarizes the
operating boundaries.
•
(on page 5-12): Details various source-measure circuit
configurations, including Source V, Measure V, and measure-only.
•
(on page 5-19): Covers the source-delay-measure cycle and provides an
overview of sweep waveforms.
Guarding
The purpose of guarding is to eliminate the effects of leakage current (and capacitance) that can exist
between FORCE and COMMON, or between SENSE and COMMON. The driven GUARD is always
enabled and provides a buffered voltage that is at the same level as the FORCE or SENSE HI
voltage (GUARD for both SOURCE and SENSE are the same signal that is referenced in FORCE). In
the absence of a driven guard, leakage in the external test circuit could be high enough to adversely
affect the performance of the SMU or preamplifier.
Leakage current can occur through parasitic or nonparasitic leakage paths. An example of parasitic
resistance is the leakage path across the insulation in a triaxial cable. An example of nonparasitic
resistance is the leakage path through a resistor that is connected in parallel to the device-under-test
(DUT).
Section 5
Source-measure concepts