An Ultra-Low-Power Read-Out Circuit for Interfacing Novel Gas Sensors Matrices

Abstract

New gas sensing materials, like conductive polymers and nanomaterials-based composites, together with integrated circuit advancements have enabled a new paradigm in gas sensing where a matrix of different types of sensors is used to improve selectivity and sensitivity. In this paper we present a highly flexible read-out circuit for acquiring the dc resistance of the sensors in the matrix. It can measure values from 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> up to 33 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{M}\Omega $ </tex-math></inline-formula> , with a minimum SNR of 57 dB. It also offers a wide range of input configuration in terms of resistance and bias voltages to select the optimal bias point for each sensor and to accommodate a large range of sensor types. It achieves very low power consumption at a maximum current consumption of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$194~\mu \text{A}$ </tex-math></inline-formula> and an energy per conversion ranging from 1.21 nJ up to 188 nJ thanks to the optimization of the frequency of operation. The circuit was fabricated in a 180 nm bulk CMOS process and a complete characterization of the circuit is presented including current consumption, signal-to-noise ratio, and transfer function. Finally, the circuit was tested in a real application for the measurement of NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> and NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> using two different types of sensors validating the design objectives and the capability of the read-out circuit for system-on-chip integrations.