CCII-Based Linear Ratiometric Capacitive Sensing by Analog Read-Out Circuits

摘要

Two electronic interfaces performing a differential (or ratiometric) sensor capacitance to voltage conversion are here presented. The output signal is proportional to the measurand variation x. The two read-out circuits differ themselves in their input stage: the first has an input current-to-voltage conversion, while the second one employs an input voltage source. Both of the solutions utilize commercial second generation current conveyors (CCIIs) as active blocks, in particular AD844. Theoretical analysis, simulated and experimental results have shown a good accuracy. Considering a capacitance variation due to the relative distance change, interface sensitivity (5) and resolution (res) values are constant and satisfactory: for the first solution, S = 8.54 V/μm and res = 674 pm (capacitance resolution value is 89.85 fF, that is -79 dB), while, for the second one, S = 8.13 V/μm and res = 814 pm (capacitance resolution value is 108.5 fF, that is -77 dB).