A Supply-voltage driving scheme for grounded capacitive sensor front-ends

Abstract

n this article, a novel supply-voltage driving1 (SVDR) scheme for capacitive sensor front-ends is proposed to2 eliminate the parasitic capacitance effects. The suggested circuit3 is intended for remote sensors (and, hence, connected to the4 circuit through a shielded cable) with one electrode grounded5 and of low capacitance (in the 0–10-pF range). The effects of6 the parasitic capacitance of the cable are avoided using the7 active-shielding technique, whereas those of the amplifier input8 through a smart driving of the reference node of the amplifier9 supply voltage. Thanks to these techniques, the input–output10 characteristic shows, without applying any adjustment and/or11 calibration, an offset error lower than 3 fF. The nonlinearity12 error (NLE) is in the order of 0.01% of the full-scale span (FSS),13 which corresponds to 1 fF. Different operational amplifiers (OAs)14 and different lengths (up to 15 m) of the interconnecting cable15 are experimentally tested to demonstrate the feasibility of the16 circuit. In comparison with similar circuits recently suggested in17 the literature, the proposed circuit does not require any bulky18 component, such as a transformer, and consequently, it is a19 lower-cost solution and suitable to be integrated.