Energy efficient integrated gas sensor system with post CMOS functionalization

Abstract

An energy efficient gas sensor array is presented in 0.35 μm CMOS technology. It contains an array of 27 sensor pixels which can be functionalized with a distinct gas sensing material. A sensor pixel is capable of extracting the impedance of the sensor upto 10 KHz. Each pixel contains digitally programmable gain stages for sensor signal amplification. The amplified signal is subsequently digitized using a second order continuous time delta sigma (CT-ΔΣ) modulator. CT-ΔΣ modulators are low power alternatives to discrete time (DT) ΔΣ modulators. Fully differential approach of signal amplification and digitization reduces the effect of process variations. The chip also contains a reference pixel to compensate for the phase shift introduced by the signal processing circuits. An proportional to absolute temperature sensor with digital readout is provided on chip to measure the ambient temperature. A sensor pixel of the chip is functionalized with polycarbazole conducting polymer to sense volatile organic gases at room temperature. Measurement results on exposure to toluene are presented. The chip consumes only 57 mW from 3.3 V supply. An graphical user interface and a microcontroller interface is designed to establish communication between the chip and a computer for chip calibration, data acquisition and analysis.