Abstract
A high-performance current generator for the picoampere region is presented. Although it was primarily developed as a part of an automatic test system to calibrate charge integrators for accelerating machines, it can suit a wide range of applications. It consists basically of a positive feedback loop of controlled gain which includes a varactor bridge operational amplifier. The essential features of the instrument are a 1 pA resolution and a 10 15 Ω output impedance. The output is guarded and floating between −120 V and + 120 V, and the voltage across the external load is measured without affecting the delivered current by a digital panel meter on the front panel. The unit can therefore operate as a high-accuracy do impedance meter.
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