A traceable precision current source for currents between 100 aA and 10 pA. - Gerd-Dietmar Willenberg; H. N. Tauscher; Peter Warnecke (IEEE Trans. Instrum. Meas., 2003)

Novel Digital Voltage Ramp Generator for Use in Precision Current Sources in the Picoampere Range. - Gerd-Dietmar Willenberg; H. N. Tauscher (IEEE Trans. Instrum. Meas., 2009)