A SWITCHED-CAPACITOR INTERFACE FOR CAPACITIVE SENSORS BASED ON RELAXATION-OSCILLATORS

A new switched-capacitor (SC) interface for capacitive sensors has been proposed based on a modified Martin’s relaxation oscillator. The output signal is the duty cycle of a pulsewidth modulated square-wave voltage or a binary-coded digital signal which is directly related to the capacitance ratio of an unknown capacitance Cx and a reference capitance Cr. The circuit can be implemented in a monolithic IC form using presently available CMOS technology. It requires a relative small device count integrable onto a small chip area and it is suited particularly for the on-chip interface circuitry for microprocessors. © 1990 IEEE