Novel Digital Voltage Ramp Generator for Use in Precision Current Sources in the Picoampere Range

摘要

We report on the development of a novel highly linear voltage ramp generator to be used for the traceable calibration of picoamperemeters. The generator is based on two digital-to-analog converters, one of them being used to compensate for the differential nonlinearity of the other one. The generator is completely controllable by a computer, its voltage slope $dV/dt$ is adjustable between 1 and 1000 mV/s. During a ramp running between $-$10 and $+$10 V, the slope shows a relative variation of only $1.3 cdot 10^{-5}$ (relative standard deviation). Due to a small output filter time constant of only 10 ms, we are, for the first time, able to conduct dynamic measurements of picoamperemeters with no sacrifice of linearity.