Comparison of Low DC Current Traceability Methods and Gas Capacitors AC–DC Dependence

partially_open6sìThis article compares two instruments for the traceable measurement of dc low currents, a custom capacitance-voltage (C-V) source and the ultrastable low-current amplifier (ULCA), a commercial precision transresistance amplifier. The instruments are calibrated through independent traceability routes. The comparison base relative accuracy is in the 10(-6)-10(-5) range. Differences between the two instrument readings, in the 10(-5) range, are interpreted as an effect of the frequency dependence of the capacitor employed in the C-Vsource. Such frequency dependence can also affect primary metrology experiments in other fields.openCallegaro, Luca; Cassiago, Cristina; D'Elia, Vincenzo; Gasparotto, Enrico; Enrico, Emanuele; Gotz, MartinCallegaro, Luca; Cassiago, Cristina; D'Elia, Vincenzo; Gasparotto, Enrico; Enrico, Emanuele; Gotz, Marti

Calibration Setup for Ultralow-Current Transresistance Amplifiers

We describe a setup for the calibration of the transresistance gain 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 calibrated transresistance is traceable to the units of capacitance and time. Two different calibration modes were tested: with dc current (obtained using a custom-made piecewise linear ramp generator) and with low-frequency sinewave current (using a commercial generator). The relative base accuracy of the implementation is in the 10⁻⁵ range