Generation of Reference DC Currents at 1 nA Level With the Capacitance-Charging Method

The capacitance-charging method is a well-established and handy technique for the generation of dc current in the 100 pA range or lower. This method involves a capacitance standard and a sampling voltmeter, highly stable devices easy to calibrate, and it is robust and insensitive to the voltage burden of the instrument being calibrated. In this paper, we propose a range extender amplifier, which can be employed as a plug-in component in existing calibration setups, and allows the generation of currents in the 1 nA range. The extender has been employed in the Istituto Nazionale di Ricerca Metrologica setup and validated with two comparisons at 100 pA and 1 nA current levels. The calibration accuracy achieved on a top-class instrument is 5 × 10^-5 at 1 nA.