Design of the Sensor CMOS Interface for 8×8 CNT Gas Sensor Array

Design of the Sensor CMOS Interface for 8×8 CNT Gas Sensor Array
Carbon nanotube (CNT); Sensor CMOS interface; Gas sensor
Issue Date
Asian Conference on Chemical Sensors
, 1-1
This paper presents design of the sensor CMOS interface for 8×8 CNT gas sensor array. The sensor interface chip shown in figure1 consists of a 8×8 input current source array, multiplexers, a 8bit-DAC, a digital controller, and a universal asynchronous receiver/transmitter( UART). An input current source is sequentially changed by the digital controller to obtain reasonable resistance resolution according to the variation of the sensor resistance. In [1-2], interface uses op-amps to increase the dynamic range, but can result in higher power consumption. Therefore, we suggest an architecture that does not require an op-amp. Also, the input current source and comparator are selectively activated by digital controller to save power. The 8bit-DAC uses a new architecture that consists of two 4bit-DACs, a unit gain buffer, and a common-source stage. This DAC is comparable to the conventional segment DAC[3], which has the advantage of the glitch reduction and small area by using the differential DAC cell and resistance ratio. The proposed sensor interface chip is designed with a 0.18-μm CMOS process, and consumes maximum 18mW at sampling rate(81.2kS/s) of the comparator. The designed interface chip achieves simulation accuracy of under 0.5% error across the 10kΩ~1MΩ range.
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