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Integrating metal-oxide-decorated CNT networks with a CMOS readout in a gas sensor.

Lee H, Lee S, Kim DH, Perello D, Park YJ, Hong SH, Yun M, Kim S - Sensors (Basel) (2012)

Bottom Line: The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy.The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way.The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, Seoul National University, Seoul, Korea. hyunjoong.lee@amic.snu.ac.kr

ABSTRACT
We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures.

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Analog to digital TDC circuit in the CNT ROIC.
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f9-sensors-12-02582: Analog to digital TDC circuit in the CNT ROIC.

Mentions: The resolution of this type of TDC is determined by the length of a clock cycle. This resolution can be improved by multiplying the clock frequency, but power consumption is directly proportional to this frequency. Instead, we combine a DLL-based fine TDC with a counter-based coarse TDC as shown in Figure 9. A DLL is used to generate multi-phase clock signals in the fine TDC. Once the DLL is locked, assuming there is no harmonic lock problem, the DLL output clock is delayed by a single clock cycle with respect to the input clock. Thus the delay produced by each cell in the DLL is a clock period divided by the total number of delay cells. The START and STOP signals sample the clock phases and cause the states of the delay-line to be stored in registers. These states fix times of arrival of the START and STOP signals within the clock period. The sampled code is changed to binary, and then added to, or subtracted from, the clock cycle counter code. Figure 10 shows the operation of the fine TDC diagrammatically, using 4 delay cells. The actual design has 16 delay cells.


Integrating metal-oxide-decorated CNT networks with a CMOS readout in a gas sensor.

Lee H, Lee S, Kim DH, Perello D, Park YJ, Hong SH, Yun M, Kim S - Sensors (Basel) (2012)

Analog to digital TDC circuit in the CNT ROIC.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3376610&req=5

f9-sensors-12-02582: Analog to digital TDC circuit in the CNT ROIC.
Mentions: The resolution of this type of TDC is determined by the length of a clock cycle. This resolution can be improved by multiplying the clock frequency, but power consumption is directly proportional to this frequency. Instead, we combine a DLL-based fine TDC with a counter-based coarse TDC as shown in Figure 9. A DLL is used to generate multi-phase clock signals in the fine TDC. Once the DLL is locked, assuming there is no harmonic lock problem, the DLL output clock is delayed by a single clock cycle with respect to the input clock. Thus the delay produced by each cell in the DLL is a clock period divided by the total number of delay cells. The START and STOP signals sample the clock phases and cause the states of the delay-line to be stored in registers. These states fix times of arrival of the START and STOP signals within the clock period. The sampled code is changed to binary, and then added to, or subtracted from, the clock cycle counter code. Figure 10 shows the operation of the fine TDC diagrammatically, using 4 delay cells. The actual design has 16 delay cells.

Bottom Line: The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy.The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way.The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, Seoul National University, Seoul, Korea. hyunjoong.lee@amic.snu.ac.kr

ABSTRACT
We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 μm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures.

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