Method for Measuring Small Nonlinearities of Electric Characteristics

Abstract

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.