A CCII-based non-inverting Schmitt trigger and its application as astable multivibrator for capacitive sensor interfacing

This paper presents a novel second-generation current conveyor (CCII)-based non-inverting Schmitt trigger topology. By means of the use of only three resistances, it is possible to set easily the threshold values or, in addition, the trigger can be set also to work as a zero-voltage comparator. The theoretical working principle has been confirmed through PSpice simulations implementing an integrated CCII, designed in a low-cost standard complementary metal-oxide-semiconductor technology (Austria Micro Systems (AMS) 0.35μm) with low-voltage low-power characteristics, and then by experimental tests on the fabricated printed circuit board prototype through the use of the commercial component AD844 (Analog Devices) as CCII. As its main application example, the presented trigger has been employed to implement an astable multivibrator proposed here as a capacitive sensor interface capable to accurately detect about five decades of capacitive variations in the range of [100pF-5.5μF] with a maximum relative error lower than ±10%.