Agilent Technologies 4338B, Operation Manual

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Theory of Operation 4338B
T est Signal Level
A ctual Signal Level across DUT
Most components have impedance characteristics that are dependent on the applied signal
level. So , the test level setting must be set appropriate for the DUT .
Figure 3-11. Simplied Model of 4338B
Figure 3-11 shows a simplied model of the 4338B . The 4338B can select test current levels of,
1A, 10A, 100A, 1mA, and 10 mA. The selection of test signal level decides the 4338B 's test
voltage source level, Vs , and its source resistance , Rs , as follows:
T able 3-4. Source V oltage and Source Resistance
Level 1A 10A 100A 1mA 10 mA
V
S
11mV 110mV
R
S
11110 1110 110 10.1 10.1
The signal level across the DUT depends on the test voltage source level, Vs , the source
resistance of the 4338B, Rs , and the impedance of the DUT ,R
DUT
, as follows:
I =
V s
R s + R
D U T
If the DUT's resistance is low enough to be assumed as 0 when compared with Rs , the test
current level, I, will be close to the selected level. If DUT's resistance is high and cannot be
assumed to be 0 when compared with Rs , the test signal level will dier from the selected
test signal level. F or example , to measure resistance 20 , with a 100 A test signal level, the
actual signal level across the DUT will be 85 A (
11 mV
110+20
).
Limitation of T est Level
The 4338B automatically sets the test signal level to 0 V when the test voltage across the DUT
exceeds 20 mV. F or more information, see \Dry Circuit Loop " in Chapter 7.
3-22 Function Reference
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