A low noise source for DC voltage ratio calibration of DVMs

Owing to their uttermost linearity, high-grade multimeters can be profitably used as voltage ratio standards. To exploit the high performances achievable, the residual nonlinearities must be evaluated with a quantum reference and particular attention is required to avoid reduction in accuracy. Differently from the resistive divider case, the ratio is obtained from actual voltage measurements, and the noise of the voltage source is consequently an important contribution to the uncertainty. In the following we report on a low noise, floating, DC voltage source with advantages compared to currently available solutions. The output voltage, controlled by a pc through an isolated link, allow to span the whole DVM range with highest accuracy.