Research on the calibration of pA weak current instruments

A pA current source is designed for the calibration of weak current measuring instruments. According to the measuring principle of weak current, a design scheme of weak current source based on a high value resistance is proposed. The thermal noise of output resistance is analyzed, and the resistance must be high enough. The characteristics of input port in weak current measuring instruments is analyzed, whose input port voltage is a main factor effecting the accuracy of weak current source. So the source voltage and the value of output resistance are calculated. The test results indicate that the accuracy of the pA weak current source is better than ±3%, which range between ±1 pA and ±200 pA, and satisfies the calibration need of pA weak current measuring instruments. (authors)