was selected to supply input current signal to the picoammeter
with a model 7078 triax cable. The outputs of the two sections of
the circuit were both fed into a 14-bit NI PXI-6133 ADC card which
was controlled by the DAQ software developed using LabWindows/
CVI.
Specifications of the picoammeter and the GI are shown in
Tables 1 and 2. Parameters such as conversion gain, linearity error
and noise were measured when the current source was in DC mode
and filtered. The sample interval of the ADC was 100 ls. All DC test
results presented here, including linearity of the two sections
shown in Figs. 7 and 8, were based on the average of more than