Capacitance measurement based on an operational amplifier circuit: error determination and reduction

Errors introduced in an operational-amplifier-based sine-wave oscillator applied in capacitance measurement are considered. The errors due to the nonideal characteristics of the operational amplifier are addressed. The oscillator circuit was simulated using the SPICE program, and gives the opportunity to study the behavior of the circuit under nonideal conditions, and to estimate the errors introduced in the measured capacitance and the frequency of oscillation. It is shown that major sources of error are the gain-bandwidth product and the output resistance of the operational amplifier. Compensation techniques to reduce errors related to the gain-bandwidth product are presented. Experimental results confirming the error reduction are included