Noise measurements in MOS transistor and vibrating-capacitor electrometers

Abstract

The noise behaviour of two types of electrometer is described. Values of the power spectral densities of the noise sources are derived from measurements, using a suitable theoretical model. For an MOS electrometer the input voltage noise density was found to have a value close to those reported elsewhere, although the dominant source of electrometer noise is shown to be a current noise source at the gate of the MOS transistor, which has not been extensively studied previously. In the case of the vibrating-capacitor electrometer a current noise associated with the vibrating capacitor was observed, the source of which is not clear. The amplitude distribution of the noise was also studied experimentally and found to be significantly non-Gaussian.