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.
been used. However, a radio-frequency carrier can be used easily by replacing the l-kHz oscillator with a radiofrequency oscillator and by redesigning the peak detector only. The rest of the circuits will remain the same since the signals at these stages are of low (modulating) frequency.VII. CONCLUSION A simple feedback scheme for controlling the amplitude of oscillators by means of a voltage has been described. The control is precise and linear. Two applications ofthe scheme have been considered; one in amplitude stabilization of oscillators and the other in generation of stabilized amplitude modulation. The experimental results agree closely with theoretical predictions.In the examples discussed in the paper, the scheme stabilized the amplitude of oscillation against variations with respect to frequency. However the stabilization will remain effective against variation due to
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