Externally Referenced Current Source With Stability Down to 1 nA/A at 50 mA

The noise and stability of a current source are limited by the quality of components used for construction, such as the voltage reference chips, resistors, and power supplies. A state-of-the-art commercial current source typically exhibits a stability no better than parts in 10⁷. In this paper, we present a way to implement a current source with ``external'' electrical references. This approach allows the current source stability to be decoupled from the noise characteristics of the main power supply circuit. Stability of about a few parts in 10⁹ in a day has been reached at 50 mA, representing the most stable current source at the milliampere range to date.