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This paper presents an energy-efficient chemical sensor system that uses carbon nanotubes (CNT) as the sensing medium. The room-temperature operation of CNT sensors eliminates the need for micro hot-plate arrays, which enables the low energy operation of the system. An array of redundant CNT sensors overcomes the reliability issues incurred by the CNT process variation. The sensor interface chip is designed to accommodate a 16-bit dynamic range by adaptively controlling an 8-bit DAC and a 10-bit ADC. A discrete optimization methodology determines the dynamic range of the DAC and the ADC to minimize the energy consumption of the system. A simple calibration technique using off-chip reference resistors reduces the DAC non-linearity. The sensor interface chip is designed in a 0.18-mum CMOS process and consumes, at maximum, 32 muW at 1.83 kS/s conversion rate. The designed interface achieves 1.34% measurement accuracy across the 10 kOmega-9 MOmega range. The functionality of the full system, including CNT sensors, has been successfully demonstrated.