Correlation spectrum analyzer: Principles and limits in noise measurements

The paper describes the principles of operation and the expected performance of correlation spectrum analyzers in the detection and measurement of stationary noise produced by passive or active devices under test (DUT). It is shown that a sensitivity of few pV/rootHz in voltage noise measurements and of few fArootHz in current noise measurements may be reached with a properly long measurement time rarely exceeding few hours. The paper highlights the role of the DUT impedance and of the amplifiers noise sources in setting the sensitivity limit of the instrument as given by the generation of spurious correlated signals that feed both channels.