A highly linear current-mode phase-based differential readout for interdigitated capacitive gas sensors

Le résumé fourni par la source

Capacitive sensors based on interdigitated electrodes (IDCs) represent a solution for highly sensitive detection of environmental gases, thanks to their strong dependence on dielectric variations induced by analyte adsorption. This work presents an IDC-based gas sensor functionalized with a hydrogel-based sensitive layer, together with a dedicated analog readout circuit. The sensing mechanism relies on the modulation of the effective permittivity of the functional layer upon gas exposure, resulting in capacitance variations in the sub-picofarad range. These variations (to 27 pF, from a baseline of 9 pF) are converted into measurable voltage signals through a differential phase-shift architecture, based on the Second-Generation Voltage Conveyor (VCII), allowing inherent rejection of common-mode electrical disturbances and reduced sensitivity to parasitic effects. Thanks to the intrinsic linear phase response around the operating point, the sensor system achieves a highly linear capacitance-phase-voltage transduction over the experimentally investigated range, with a coefficient of determination of approximately 𝑅 2 = 0 . 9 9 7 , simplifying calibration and improving accuracy. Parametric simulations of a CMOS VCII implementation show a capacitance-to-voltage sensitivity of 1.81 mV/pF and a resolution of 0.019 pF. Experimental results on a PCB prototype, based on the AD844, configured as a VCII, confirm the approach, with sensitivity around 103.31 mV/pF and a minimum detectable capacitance variation of approximately 0.33 pF. Gas sensing experiments demonstrate promising performance for H₂O, O₂, and CO₂ detection, under controlled laboratory conditions, in terms of sensitivity and resolution, confirming the feasibility of the proposed approach as a highly linear laboratory-scale platform for capacitive gas-sensing investigations.

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