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Applications
HI
LO
Model 230
Voltage Source
= Closed Crosspoints on 7174A Card (Figure 3-5).
Figure 3-6
System configuration for measuring common-emitter characteristics
3.3.2 Testing common-source characteristic of
FETs
The system shown in Figure 3-5 could be used to test a vari-
ety of characteristics including I
and V
. To demonstrate a practical use for the system,
DS[OFF]
we will show how it can be used to generate common source
characteristic curves of a particular JFET.
In order to generate these curves, the instrument must be
connected to the JFET under test, as shown in Figure 3-6.
The advantage of using the matrix is, of course, that it is a
simple matter of closing specific crosspoints. The cross-
points that must be closed are also indicated on the diagram.
To run the test, V
is set to specific values, for example in
GS
increments of 0.25V. At each V
voltage (V
) is stepped across the desired range, and the
DS
drain current, I
, is measured at each value of V
D
data are compiled, it is a simple matter to generate the
common-source IV curves, an example of which is shown in
Figure 3-7. If the system is connected to a computer, the test
and graphing could all be done automatically.
3-6
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D
F8
F10
G
V
S
GS
E9
E11
, I
, I
, I
,
GSS
D[OFF]
G[ON]
DSS
value, the drain-source
GS
. Once all
DS
Electrometer/Source
A12
B9
I
D
D9
V
DS
C11
10 0
9 0
8 0
7 0
6 0
I
D
(µA)
5 0
4 0
3 0
2 0
1 0
0
0
1
2
3
Figure 3-7
Typical common-source FET IV characteristics
617
HI
Meter
(Current)
LO
HI
Voltage
Source
LO
V
= 0V
GS
V
= -0.5V
GS
V
= -1V
GS
10
4
5
6
7
8
9
V
(Volts)
DS
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