An automatic C-V plotter

Abstract

A C-V plotter is described which employs a novel current sensing circuit to enable plotting of incremental capacitance, dQ/dV, as a function of bias voltage. The main advantages of this current sensing circuit are that the output voltage (which is proportional to the capacitive current through the capacitor under test) is in phase with the applied voltage and that its magnitude is independent of frequency. The product of the output and the applied voltage at any signal frequency therefore contains a DC term which is proportional to the capacitance. Design equations are given which enable the components of this circuit to be selected. A complete measurement system based on this circuit is then described and details of particular circuits are given.