ULTRALOW-NOISE PROGRAMMABLE VOLTAGE-SOURCE

To avoid introducing additional noise sources while making low-frequen cy noise measurements, batteries are normally used instead of electron ic power supplies. This paper presents an alternative solution by desc ribing the design, construction, and testing of an ultralow-noise volt age source. Such a power supply can be computer controlled and has a t ypical noise level two orders of magnitude below that of similar comme rcial instruments. Some typical values of the spectral density of the voltage fluctuations at its output are: (10(-12), 10(-15), 10(-16)) V- 2/Hz at (0.01, 0.1, and 1) Hz, respectively. These noise performances are almost independent of the supplied current, with a degradation of less than 3 dB up to 400 mA, A special algorithm for digital-to analog conversion, using passive devices with 1% tolerance, ensures a resolu tion of 2.5 mV and an accuracy better than +/-1.5 mV over the entire o utput range from 0 to 8 V.