Very low-noise, high-accuracy programmable voltage reference

We have designed and tested a very low-noise, high-accuracy programmable voltage reference that is intended as an alternative to batteries for the realization of automated low-frequency noise measurement systems. The output voltage, which can be set via a built-in RS232 interface, ranges from 0 to 5 V with a resolution and long-term stability of +250 (mu)V. The power spectral density of the output voltage fluctuations is less than 2.10/sup -16/ V/sup 2//Hz at 100 mHz and remains below 10/sup -17/ V/sup 2//Hz above 1 Hz.