A New High-Speed Method of Testing Capacitors

A new high-speed method of determining the capacitance and a quantity which the writers call the pulse series resistance (PSR) of an unknown capacitor is presented. The unknown capacitor is assumed to consist of an ideal capacitor and a series resistor. The test circuit consists of a low-impedance driver, a low-loss coupling capacitor, and a wide-band high-input/low-output impedance video-type amplifier. The unknown capacitor is placed in a negative feedback loop of this amplifier. The input waveform is a trapezoid. The output waveform contains information that is indicative of the capacitance and PSR of the unknown capacitor. The information is obtained by measuring two voltages, one of which is completely independent of the other. Capacitors were measured from approximately 2 pf to 2 μf with an accuracy of ±5 per cent. The PSR was not available for capacitors less than 100 pF because of test-circuit limitations. The capacitance and PSR of an unknown capacitor could be made available within 500 μsec with modern voltage-measuring and calculating techniques.