A programmable second order oversampling sigma-delta analog-to-digital converter (ADC) is designed and fabricated in
0.5 μm n-well CMOS process for low-power interface electronics of a sensor node in wireless sensor networks. The
sigma-delta ADC can be programmed to operate at three different oversampling ratios of 16, 32, and 64 to give three
different resolutions of 9, 12 and 14 bits, respectively which impact the power consumption of the sensor module. The
major part of power is consumed in the decimator of the ADC by the integrators which operate at the highest sampling
rate. Hence, an alternate design is introduced in the integrator stages by inserting sign extension coder circuits and
reusing the same integrators for different resolutions and oversampling ratios. The programmable ADC can be interfaced
with on or off-chip nanosensors for detection of traces of toxic gases and chemicals.
An attempt has been made to design a CMOS single-chip chemical detection system for integrating nanocantilevers with low power readout electronic circuits for the detection of traces (few molecules) of hydrocarbon-based gases in the environment. The design is divided into two following building blocks: nanocantilevers as chemical sensors and readout electronics. Carbon nanotubes (CNT)-based cantilevers have been chosen for high-sensitivity chemical sensing for on-chip integration with the interface electronics. An experimental technique is presented for the fabrication of CNT cantilever beams. Design of a readout interface electronics using a switched capacitor technique is presented in 0.5 μm n-well CMOS process for integrating CNT cantilever sensors.