Keithley Series 2600 User Manual

3-6
SECTION 3
Bipolar Transistor Tests
3.5 Current Gain
The following paragraphs discuss two methods for determining
DC current gain, as well as ways to measure AC current gain.
3.5.1 Gain Calculations
The common-emitter DC current gain of a bipolar transistor is
simply the ratio of the DC collector current to the DC base current
of the device. The DC current gain is calculated as follows:
I
C
ß =
__
I
B
where: ß = current gain
I
C
= DC collector current
I
B
= DC base current
Often, the differential or AC current gain is used instead of the
DC value because it more closely approximates the performance
of the transistor under small-signal AC conditions. In order to
determine the differential current gain, two values of collector
current (I
C1
and I
C2
) at two different base currents (I
B1
and I
B2
) are
measured. The current gain is then calculated as follows:
∆I
C
ß
ac
=
___
∆I
B
where: ßa = AC current gain
∆I
C
= I
C2
– I
C1
∆I
B
= I
B2
– I
B1
Tests for both DC and AC current gain are generally done at one
specific value of V
CE
. AC current gain tests should be performed
with as small a ∆I
B
as possible so that the device remains in the
linear region of the curve.
3.5.2 Test Configuration for
Search Method
Figure 3-5 shows the test configuration for the search method of
DC current gain tests and AC gain tests. A dual-channel System
SourceMeter instrument is required for the test. SMUB is used
to supply I
B1
and I
B2
. SMUA sources V
CE
, and it also measures the
collector currents I
C1
and I
C2
.
3.5.3 Measurement Considerations
When entering the test base currents, take care not to enter values
that will saturate the device. The approximate base current value
can be determined by dividing the desired collector current value
by the typical current gain for the transistor being tested.
3.5.4 Example Program 6A: DC Current
Gain Using Search Method
Use Program 6A to perform DC current gain tests on bipolar tran-
sistors. Proceed as follows:
With the power off, connect a dual-channel System Source-1.
Meter instrument to the computer’s IEEE-488 interface.
Connect the test fixture to both units using appropriate 2.
c a b l e s .
Turn on the System SourceMeter instrument and allow the 3.
unit to warm up for two hours for rated accuracy.
I
V
Series 2600
System
SourceMeter
Channel A
Source V
CE
,
Measure I
C
Series 2600
System
SourceMeter
Channel B
Set I
B
for
desired I
C
VI
V
CE
Test
Fixture
Transistor
Under Test
Output HI
Output HI
Output LO
Output LO
I
B
I
C
Figure 3-5. Test configuration for current gain tests using search method

Keithley Series 2600 Specifications

General

Brand	Keithley
Model	Series 2600
Category	Measuring Instruments
Language	English