Abstract
This paper presents a method for measuring very low currents by using the improved condenser charging method. The voltage change during the charging process of the condenser is measured on a fixed time interval by the charge sensitive amplifier and the resulting output pulses are integrated individually. The errors, which arise from a stray capacitance of the input circuit and the charge generated at the contact of the dry-reed switch, could be minimized by this method. This picoammeter has a noise level of as low as 6fA and 2fA when the internal resistance of the current sources are 1010Ω and 1011Ω respectively.
