Analysis, design and application of a capacitance measurement circuit with wide operating frequency range

A novel high frequency, low cost circuit for measuring capacitance is proposed in this paper. This new capacitance measuring circuit is able to measure small coupling capacitance variations with high stray-immunity. Hence, it could be used in many potential applications such as measuring a metal fill time in the lost foam casting (LFC) process and electrical capacitive tomography (ECT) system. The proposed circuit is based on differential charging/discharging method using current feedback amplifier and a synchronous demodulation stage. The circuit has a wide high frequency operating range with zero phase shift; hence multiple circuits can work at different frequencies simultaneously to measure the capacitance. The non-ideal characteristics of the circuit has been analyzed and verified through LTSpice simulation. Results from the tests on a prototype and a simulation elucidate the practicality of the proposed circuit.