A Transistorized Low Capacitance Meter

ABSTRACT

Frequently the depletion layer capacitances of transistors and other semiconductor devices have to be measured under their operating conditions, prior to their incorporation in different circuits. This is necessitated because of the wide production spreads in this parameter. The conventional bridge methods of use in the measurements of passive capacitances in the same range as these are not suited for this application, because they employ large signal voltages across the unknown capacitance. With such limitations in view, a simple and cheap transistorized low capacitance meter capable of rapidly measuring all capacitances in the range 0·3–30 pF., and in particular the depletion layer capacitances of semiconductor devices under their operating conditions is developed and described. It employs the well-known principles of FM detection for accurately determining the frequency shift of a HF oscillator, which does not seem to have attracted the attention in the development of instruments for this purpose. The power consumption of the instrument is less than 4 m A. at 9 volts. The instrument measures 125×110×160 mm. overall and weighs about 1·5 kg.