Uncalibrated operational amplifier‐based sensor interface for capacitive/resistive sensor applications

Abstract

In this paper, a new configuration of operational amplifier-based square-wave oscillator is proposed. The circuit performs an impedance-to-period (Z-T) conversion that, instead of a voltage integration typically performed by other solutions presented in the literature, is based on a voltage differentiation. This solution is suitable as first analogue uncalibrated front-end for capacitive and resistive (e.g. relative humidity and gas) sensors, working also, in the case of capacitive devices, for wide variation ranges (up to six capacitive variation decades). Moreover, through the setting of passive components, its sensitivity can be easily regulated. Experimental measurements, conducted on a prototype printed circuit board, with sample passive components and using the commercial capacitive humidity sensor Honeywell HCH-1000, have shown good linearity and accuracy in the estimation of capacitances, having a baseline or reaching a value ranging in a wide interval [picofarads-microfarads], as well as, with a lower accuracy, in the evaluation of more reduced variations of resistances, ranging from kiloohms to megaohms, also when compared with other solutions presented in the literature.

A Readout System for High Speed Interface of Wide Range Chemiresistive Sensor Array

“…Microcontroller Interface (DMI) [21]- [24], and quasi digital schemes namely, resistance to frequency, pulse width or period conversion [27]- [28].…”

“…Hence, this solution is not suitable for readout system that requires a fast transient response from a high density sensor array with wide resistance range. The quasi digital system converts resistance to frequency, period, or pulse width variation; but another interface circuitry is necessary to covert the quasi digital output to digital, which makes the system complex [27]- [28]. In DMI technique, the microcontroller unit (MCU) excites a passive resistive [21]- [22] or capacitive [23] sensor and then measures the duration of the transient response to reach a predefined threshold using the embedded digital timer.…”

Effect of Ni and Al doping on structural, optical, and CO2 gas sensing properties of 1D ZnO nanorods produced by hydrothermal method

“…The CO 2 gas constituting 76% of the increasing greenhouse gas effect is used in the detection of air quality and in fact has an important role on the global warming (Lin & Fan, 2020; Zhang, Qin, Zhang, Lü, & Hu, 2017). It is observed that the surface acoustic wave, capacitive, infrared, resistive, and solid electrolyte sensors are used to sense the CO 2 gas (Baraton, 1996; Bianchetti, Arrieta, & Walsöe De Reca, 2015; De Marcellis, Ferri, & Mantenuto, 2015; Nieuwenhuizen & Nederlof, 1990; Takeda et al, 2015; Wang et al, 2016). In the resistive sensors, as a result of the interaction of the target gas with the surface, the conductivity (resistance) of sensor material changes and thus an automatically stimulating effect occurs (Hadia, Alqahtani, & Mohamed, 2015).…”

“…Similarly, some characteristic properties such as nontoxicity, chemical stability, large area deposition, low‐cost, environmental compatibility, controllability of compositions, uniformity of thickness, photo‐sensitivity/catalytic activity, and tailoring of nanostructures. As well known that for the ZnO nanorod productions there are several deposition methods as regards as the magnetron sputtering (Lin & Fan, 2020), one‐step solid state reaction (Takeda et al, 2015), spray pyrolysis (De Marcellis et al, 2015), electrodeposition (Wang et al, 2016), partly sol–gel (Hadia et al, 2015; Li, Shi, & Hu, 2017), chemical vapor deposition (Jagadale, Patil, Vanalakar, et al, 2018; Patil et al, 2016; Zhang, Qin, et al, 2017), pulsed laser deposition (Nieuwenhuizen & Nederlof, 1990), and hydrothermal (Baraton, 1996; Bianchetti et al, 2015). Among the fabrication processes, the latter method (related to the ZnO nanorods formation on the seed layer [Anajafi, Naseri, & Neri, 2020; Ghosh, Zhang, Zhang, & Shi, 2019; Samarasekara, Yapa, Kumara, & Perera, 2007]) exhibits superior features including the simplicity, cost effectiveness, large area deposition, and flexibility in the compositional modification.…”

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

“…In particular, the impedance‐to‐period (Z‐T) conversion becomes suitable in those applications (e.g. sensor interfaces) where a wide variation range and/or a not well‐known baseline occur , while for reduced variations, an impedance‐to‐voltage (Z‐V) conversion is preferred .…”