A CCII-based relaxation oscillator as a versatile interface for resistive and capacitive sensors

In this paper, a novel Current-Mode (CM) square/triangular wave oscillator, based on second generation current conveyor (CCII), operating as resistance/capacitance to time conversion is described. The proposed oscillator, which consists of two CCII as an active element, three grounded resistances and one capacitance found to be an effective alternate of voltage mode based interfaces for wide range capacitive and resistive sensors. The interface circuit was implemented with commercially available current feedback operational amplifier AD844 from Analog Devices and passive components. Experimental results confirmed the theoretical expectations, showing good linearity in wide oscillation frequency/period range, which can be independently adjusted through resistive or capacitive external passive components. Experimental measurement was also conducted on a fabricated capacitive humidity sensor to verify the real time application of the proposed interface circuit. The interface circuit has shown a good accuracy and linearity for wide variation in capacitance of humidity sensor.