Keithley 237 Instruction Manual

Operation
4-11
DC parameter checks
With a transistor conÞgured as a common-emitter am-
pliÞer, the test system shown in Figure 4-8 can be used
to determine the following DC parameters: Collector
current (I
C
), base current (I
B
), current gain, emitter cur-
rent (I
E
) and base-to-emitter voltage (V
BE
).
Figure 4-8 shows which crosspoints to close to conÞg-
ure the ampliÞer circuit. SMU #1 is conÞgured to
source voltage and measure current. It is used to power
the collector circuit (V
CE
) and measure the collector
current (I
C
). SMU #2 is conÞgured to source current
and measure voltage. It is used to provide the base cur-
rent (I
B
) for the transistor, and will also measure the
base-to-emitter voltage (V
BE
). With collector current
(I
C
) and base current (I
B
) known, the current gain can
be calculated as follows:
The emitter current (I
E
) can be determined by using
Kirchoff’s Current Law as follows:
Gain
I
C
I
B
-----=
I
E
I
C
I
B
+=
Common-emitter characteristic curves
A proÞle of the transistor operating characteristics can
be obtained by measuring the collector current over a
speciÞed voltage range (V
CE
) for different base bias
currents (I
B
). For example, Figure 4-9 shows the charac-
teristics of a typical NPN silicon transistor at base bias
currents (I
B
) of 20 µ A, 40 µ A, 60 µ A, and 80 µ A.
Extensive trigger capabilities facilitate synchronization
of the Keithley Source Measure Unit operations. By
performing a subordinate sweep, SMU #1 will perform
a staircase sweep at every base bias current level set by
SMU #2. On every step of each staircase sweep, SMU
#1 will source a voltage level (V
CE
) and measure the
subsequent collector current (I
C
). For the characteris-
tics shown in Figure 4-9, four staircase sweeps were
performed; one staircase sweep at each base bias level.
Refer to a Keithley Source Measure Unit instruction
manual for details on performing sweeps.
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Keithley 237 Specifications

General

Brand	Keithley
Model	237
Category	Measuring Instruments
Language	English