Ultra low noise current sources

The current sources which are normally used in research laboratories are not suitable for low noise measurement systems because of the unacceptable level of low frequency noise which they introduce in the measurement chain. The most important source of low frequency noise in such instruments is the solid state device (usually a Zener diode) which is used as voltage reference. By using a novel circuital topology in which a lead battery which does not supply current is used as voltage reference, we have been able to design an ultra low noise current source characterized by a low-frequency noise level some orders of magnitude lower than that of similar commercial instrumentation. The design, realization and testing of such current source is presented.