Autoranging Compensation for Variable Baseline Chemical Sensors

This paper addresses the need for a broad-base signal conditioning module designed to process chemical sensor signals in such a way that the output of the conditioning circuits ensures similar baseline and dynamic range, regardless of fabrication variation and sensor drift. These baseline compensation circuits are demonstrated in the context of processing resistance changes from composite polymer chemical sensors and tin-oxide chemical sensors. Because of the initial highly variable baseline state of chemiresistors, a large number of bits in an A/D converter are required to translate the sensor information from an array of these sensors into a digital format for use by a microprocessor. In this work, we present a generic circuit for auto-calibrating and compensating for the baseline of a variety of chemiresistive devices in order to improve concentration measurement resolution and analyte discrimination. The measurement circuits optimize sensor resolution via baseline compensation. Dynamic range is standardized to a constant size regardless of initial baseline resistances. The resulting dynamic range can be as much as two orders smaller than an uncompensated circuit and achieve the same sensor accuracy. Simulations have also shown a factor of 68 improvement in resolution.