Method for Measuring Small Nonlinearities of Electric Characteristics
Tom Guldbrandsen, N.I. Meyer, J. Schjaer-Jakobsen · Review of Scientific Instruments · 1965
A method is described for measuring very small deviations from linearity in electric characteristics. The measurement is based on the harmonics generated by the nonlinear element when subjected to a sine wave signal. A special bridge circuit is used to balance out the undesired harmonics of the signal generator together with the first harmonic frequency. The set-up measures the small-signal value and the first and second derivative with respect to voltage. The detailed circuits are given for measuring nonlinearities in Ohmic and capacitive components. In the Ohmic case, a sensitivity in the measurement of the relative second order nonlinearity of about 5×10−8 is obtained. In the capacitive case, the sensitivity expressed in terms of the minimum measurable values of the derivatives is dC/dV = 1.5×10−17 F/V and d2C/dV2 = 2×10−16 F/V2.