A New and Fast-Readout Interface for Resistive Chemical Sensors

Abstract

The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of resistive values that the sensors can show. In addition, some sensors could have baseline resistive values up to tens of gigohms. To avoid the use of expensive picoammeters or the use of circuits adopting scaling factors, different solutions have recently been proposed, exploiting the resistance-to-time conversion (RTC) technique. They show good linearity and are suitable for the integration in a chip together with the elaboration unit, but they may require long measurement time (tens of seconds) if high resistance values need to be estimated. In addition, they may suffer the influence of a sensor parasitic capacitance, in parallel with the resistive component. In this paper, a new method is proposed to reduce the measuring time, keeping the advantages offered by the RTC approach and including a parasitic capacitance estimation feature. Particularly, an effective architecture, based on moving thresholds, has been proposed, simulated, and experimentally tested with commercial resistors (values between 1 MOhm and 100 GOhm) and capacitors (values between 1 and 47 pF). Finally, a fast sensor transient, due to a rapid change in the heating power, has been acquired with the proposed instrument and compared with a similar transient analyzed with a classical RTC approach. This test has shown the applicability of the interface for solutions requiring detailed information of the sensor response, such as the characterization of new sensors (e.g., nanowires) or the behavior analysis during nonstandard thermal profiles

Towards a Chemiresistive Sensor-Integrated Electronic Nose: A Review

“…The Second Generation Current Conveyor (CCII)-based interface was designed to operate at a low ±0.75 V supply voltage and cost only 700 μW [ 169 ]. In previous studies, a fast readout interface was designed [ 170 ], and a CMOS-integrated interface was fabricated using 0.35 μm standard CMOS technology, consumed only 600 μW at a supply voltage of 1.8 V, and cost approximately 0.9 mm 2 [ 171 ].…”

Thermal Modeling and Characterization of a Thin-Film Heater on Glass Substrate for Lab-on-Chip Applications

“…The temperature dependent convective contribution is usually neglected in first-order thermal models, that implicitly use a constant thermal resistance or conductance [3], [20]. It has been demonstrated that for temperatures sufficiently higher than the ambient temperature the thermal conductance is more accurately described by…”

Compact Current Reference Circuits with Low Temperature Drift and High Compliance Voltage

“…As described, several solutions for resistive-sensors interfacing have been proposed. To evaluate the performance of these solutions, in some cases resistive-sensors were used [ 18 ]; more often, experimental evaluations were conducted using commercial resistors to simulate the sensor over a wide resistance range [ 19 , 20 , 21 , 22 ].…”