Method and apparatus for electronically simulating capacitors

Abstract

A circuit that electronically simulates a capacitor includes a differentiator and a current source. In the preferred embodiment, the differentiator includes a differentiating gain amplifier that produces an output signal in response to an applied input signal, with the output signal being proportional to the time rate of change of the input signal. The differentiator further includes a variable inverting gain stage that produces a reference signal that has a desired phase relationship with respect to the input signal, such as a ninety degree leading phase for sinusoidal input signals. The variable gain stage is also used to provide for different simulated capacitance values, and to compensate for variations in the differentiator fixed value component. The current source is preferably a high output impedance current source such as a Howland current pump. The current source produces, in response to the reference signal from the differentiator, an output current that is proportional to the time rate of change of the input signal. The circuit also simulates dissipation factor of a capacitor in that the gain and phase response of the operational amplifiers used in the differentiator are frequency dependent. The gain stage can also be used for compensating the circuit for different applied input signal frequencies. The invention is particularly useful as a troubleshooting tool for analysis of fuel tank gauging systems.