Subpicoampere current source based on a digital-to-analog converter
A current source based on a voltage ramp generated by a 16-bit digital-to-analog converter and a differentiating capacitor has been developed in MIKES. The system is suitable for generating currents from 1 fA to 100 pA. Standard deviation of average dU/dt:s of 70 ramps during an overnight measurement is as low as 1 ppm.
Calibration setup for ultralow-current transresistance amplifiers
We describe a calibration setup for the transre-sistance of low-current amplifiers, based on the capacitance-charging method. The calibration can be performed in the current range of typical interest for electron counting experiments. The setup implementation is simple and rugged, and is suitable to be embedded in larger experiments where the amplifier is employed. The calibration is traceable to units of capacitance and of time. The base relative accuracy of the implementation is in the 10−5 range.
Highly sensitive picoampere meter
We have developed a sensitive picoampere meter for accurate room temperature measurement of currents below 10 pA. The main characteristics of the instrument are an extremely low input current, far below 1 fA, and fully automated operation. Preliminary calibration of the instrument with a separately developed facility has been done at the accuracy level of a few parts in 10/sup 4/.