A Robust Low Power Carbon Nanotube Sensor Interface Circuit in 180 nm CMOS Technology

The design and performance of a low-cost, energy-efficient carbon nanotube sensor interface circuit (SIC) is presented that is aimed at deployable/expendable applications with the sensor operating at ambient temperatures. The submicrometer SIC is designed and fabricated in CMOS 180-nm technology and consumes a maximum of 122 mu W, including a decoder and voltage follower. The SIC achieves a measurement accuracy of 1.4% over a 2.5 k Omega to 25 M Omega dynamic range of sensor resistance. A critical issue associated with a submicrometer integrated circuit implementation is satisfactory performance of the SIC for fabrication process variations that range from the slow, to typical, to fast process corners and simultaneously meeting the requirement for the very large dynamic range for sensor resistances. A robust design considering the full range of potential process variations becomes more critical as feature size is reduced. The SIC design includes an added degree for freedom for counteracting process variations during post fabrication calibration. In addition, a new design procedure is outlined and implemented to permit an accurate and efficient first order design to ensure satisfactory performance for typical, fast, and slow model parameters. The first order design is verified by complete model simulation performance, and finally selected measured results are included for a fabricated circuit.