14
Resource integration reduces
measurement error
An SMU is an instrument that combines the
capabilities of a current source, a voltage source,
a current meter and a voltage meter (along
with the capability to switch easily between
these various functions) into a single instrument.
Because the source and measurement circuitry
is closely integrated, the user can achieve far
better measurement performance with less
measurement error than would be possible by
using various independent instruments to make
the same measurement.
Feedback mechanism stabilizes
voltage and current sourcing
Since SMUs have the ability to very accurately
measure their own current and voltage output,
they have many advantages over conventional
power supplies. All SMUs have internal feed-
back loops that provide instantaneous feedback
to the sourcing circuitry, which in-turn allows the
SMU output to remain accurate and stable even
if the load conditions change unexpectedly.
Limit (compliance) feature
prevents device damage
SMUs also possess a voltage and current limit
(compliance) feature that allows the user to
set limits and to protect devices from damage
caused by excessive voltage or current. Although
the SMU normally continues to function when
it reaches the user-specifi ed limit value, it can
also be set to shutdown just like the over current
protection (OCP) and over voltage protection
(OVP) functions do on a power supply.
Accurate timing control of source
and measurement resources
The integration of the source and measure-
ment resources in an SMU allows much tighter
synchronization than would be possible with
separate instruments. Moreover, the B2900A
Series provides very fl exible triggering options
that allow the measurements points to be
defi ned independently from the sourced current
or voltage waveform. On two channel units you
can operate both channels in synchronization
or independently, and under remote control you
can trigger multiple units in unison using a group
trigger signal.
Source block:
Precision voltage and current source/
sink with sweep, pulse and AWG
capabilities. Voltage/current limit
capability is also available.
Simplifi ed block diagram of Agilent B2900A Series
Measurement block:
Precision voltage and current meter
with high speed digitizing capability.
Overview: Why use an SMU?
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