Basic Source-Measure Operation 3-11
Current measurements and capacitive loads
When measuring current in a test circuit that has high capacitance, ringing may occur. Ring-
ing is the fluctuation of current readings that is initiated by a voltage step. This fluctuation
eventually decays to a settled current reading. The higher the capacitance, the more ringing that
will occur.
Table 3-5 lists the maximum capacitive loads that the Model 6430 can accommodate effec-
tively. For the higher current ranges (1nA range and higher), the listed values represent the larg-
est capacitance in which ringing created by a voltage step will decay in less than one power line
cycle. For the lower current ranges (100pA and lower), the listed values represent the largest
capacitance that causes ringing that will settle in a reasonable amount of time.
Current measurements can be performed for higher capacitive loads as long as the increased
ringing can be tolerated. Ringing can be reduced by adding a resistor in a series with the load at
the expense of longer settling times. See
Source capacitance
in Appendix F for more
information
.
T
a
ble 3-5
Maximum capacitive loads
Current range
Maximum
Capacitive Load
100mA 0.2µF
10mA 0.2µF
1mA 0.2µF
100µA 0.04µF
10µA 3300pF
1µA 470pF
100nA 100pF
10nA 100pF
1nA 100pF
100pA 100pF
10pA 100pF
1pA 100pF
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