Current conveyor-based differential capacitance analog interface for displacement sensing application

CMOS Current Feedback Operational Amplifier-Based Relaxation Generator for Capacity to Voltage Sensor Interface

“…Capacitance sensors enable conversion of various physical changes, for instance, small distance and displacement variation [13,14,15,16] and water level detection [17], to measurable signals. Continuously operating analog interfaces for capacitance sensors use the following methods: (a) AC source-based measurements for sensing of voltage across unknown capacitance and current through unknown capacitance; (b) capacitance divider [18]; (c) resonance [18,19] and bridge circuits containing the measured capacitance [1,18,19]; (d) methods based on the transfer of charge (containing switches and their driving) [19]; (e) differential methods [13,14,15,16] ensuring high accuracy and linearity; and (f) methods based on the sensed capacity as a key part of signal generator [18,19] (sine wave oscillators and generators of other waveforms).…”

“…The last method in the previous list can be suitable for LV supply cases, because the signal processing, in comparison with direct measurement of the capacity by applied DC/AC voltage or indirect measurements expecting high voltage levels [15,16], does not depend on the voltage space (voltage levels). Compared to Refs.…”

“…Compared to Refs. [15,16], the concept proposed in this paper is simpler. Numerous works dealt with relaxation generators due to their advantages (e.g., low complexity, number of components and cost).…”

“…Differential methods, in comparison with relaxation generator-based approaches, offer higher accuracy and low measurement error (units of percent). However, these solutions [15,16] are complex. In many cases, these methods evaluate the difference of capacities but not the absolute value of capacitance.…”

“…Furthermore, various auxiliary components (e.g., control of switching, additional voltage or current sources) are necessary. The expected high output voltage levels [15,16] are not available in LV integrated solutions. Generator-based solutions of transducer are simple because enable direct transformation of capacity to frequency ( C → f 0).…”