Low-power temperature-independent CMOS measurement circuits for resistive gas sensors

Abstract

In this work, we present the design of three different circuits for the measurement of resistive gas sensors. Schematic designs of each approach are discussed and simulated using HSPICE in a commercial CMOS 180 nm technology node. Their physical layout is also implemented. The three designs output a pulsed voltage signal whose period is modulated by the resistance of the sensor. They also implement differential measurement techniques in order to reduce the effect of temperature variations. The first design uses an operational amplifier and a resistor to measure the sensor and transduce its signal; the second one employs a Wheatstone bridge with common-mode feedback and a bulk-input OTA; and the third one utilizes a current-mode Wheatstone bridge built with a current-conveyor 2. The designs consume between 1.8 and (Formula presented.) W; their temperature coefficient is always between 60 and 305 ppm/° C; and their resolution is between 0.25% and 1%. The circuits are compatible with sensors of a wide resistance range, being the best one tolerant to resistances between 2 M (Formula presented.) and 1 G (Formula presented.). Therefore, these designs are ideal for low-power autonomous applications in environments where temperature is not controlled.