A Charge Balanced C-V Converter for a Differential Capacitance Sensor

Abstract

This paper presents a simple new configuration for a switched capacitor type C-V converter based on a charge balance principle for a differential capacitance sensor and its simulation results. The new converter was devised and realized using only one operational amplifier, nine CMOS switches and an oscillation circuit. It was shown that the offset output due to the input offset voltage of an operational amplifier can be ideally reduced to zero with an appropriate additional switch configuration. By using a P-Spice circuit simulator, the offset cancellation scheme and proper transient response were confirmed for possible parasitic capacitances concerned in a typical differential capacitance sensor. In addition, a P-Spice system simulation based on analog behavioral models enabled us to reliably estimate the operation of an electro-mechanical system with the C-V converter statically and dynamically, where the electrostatic force acting on a movable electrode was taken into account.