The Environmental Sensor Readout Circuit and its Applications to Cold Chain Logistics

• Main Authors: Ho, Zih-Cheng, 賀子誠
• Other Authors: Chang, Hsie-Chia
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/82830705886931337029

碩士 === 國立交通大學 === 電子工程學系 電子研究所 === 102 === In this thesis, we present two types of readout circuits by using time-to-digital convertors (TDC). In contrast to traditional analog-to-digital converter (ADC), our approach converts the analog signal into the time pulse, and directly outputs the digital code without the voltage-to-digital or current-to-digital converter. The first type of TDCs is the differential capacitance-to-digital readout circuit. The differential readout circuit only converts the variation of differential capacitance and ignores the common-mode capacitance. Another type of TDCs is dual-DLL time-to-digital readout circuit. This circuit is used to the sensors with single-ended output. These sensors have large parasitic capacitances, and this readout circuit can compensate the parasitic capacitance and increase the sensing range with an auto-trimming mechanism. To implement the environmental sensor with our readout circuits, the differential capacitance-to-digital readout circuit is used in an accelerometer with differential finger-type electrodes. And dual-DLL time-to-digital readout circuit is used in the single-ended output sensors, humidity sensor and temperature sensors. From chip measurement results, our accelerometer can differentiate the 80-level accelerations between ±8g, and just consumes around 50uW for 1-axis, 82uW for 3-axis under 125KHz of sampling frequency with 1.8v of supply voltage. The humidity sensor is 52uW in the operating mode, and 13uW in the sleeping mode under 8KHz of sampling frequency with 1.3v of supply voltage.