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Research On The Key Techniques Of UHF RFID Tag With Embeded Temperature Sensor

Posted on:2017-04-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:L B XieFull Text:PDF
GTID:1108330485988440Subject:Communication and Information System
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Radio frequency identification (RFID) technology, which is one of the four key technologies of the internet of things (IoT), can identify objects automatically by employing wireless communication. With the advantages of long communication range, high speed, multi objects mobile identification and low cost, the UHF RFID system has been wildly applied to systems of IoT, such as intelligent logistics, traffic, anti-counterfeiting and trace. With the increasing requirements of IoT applications, network nodes with identification and sensor must be low cost, high precision, long work time, intelligent information acquisition and process with long range, which promote the naissance of UHF RFID tag with embedded high precision temperature sensor to achieve wireless temperature sensing and identification. Embedding temperature sensor into UHF RFID tag, which has negligible effect on area and cost, not only keeps the characteristics of ultra-low power, low cost, high sensitivity, miniaturization, but also features temperature sensing with high accuracy. Thus, it has vast applied prospects in warehousing of foods and medicines, cold chain logistics and temperature monitoring of power grid.According to the requirements mentioned above and based on the analysis of ISO/IEC 18000-6C standard and summery of the low power design techniques, the dissertation focuses on research of the key techniques, including the low power RF/analog/digital circuit design of passive UHF RFID tag, the low power design technique of temperature sensor, and sense-identification cooperation scheme. Then UHF RFID tag with embedded temperature sensor was implemented in 0.18μm CMOS process. The main research contributions of the dissertation are as follows:1. Key techniques of passive UHF RFID tag are researched, including voltage reference, BLF generation circuit and baseband processor. A low-power CMOS voltage reference is proposed, which employs process compensation technique to solve the impact of process variation. According to the accuracy of BLF required by ISO/IEC 18000-6C, the research on the BLF generation scheme is conducted, and two kinds of BLF generation circuits are proposed:One is BLF generation circuit with large clock variation tolerance, which utilizes clock generator with process and temperature compensation and adjusting algorithm of BLF division ratio to generate BLF required by standard and enhance the stability of the clock; The other is BLF generation circuit with dynamic adjusting technique, which employs dynamic clock calibration technique and BLF correction technique to increase the accuracy of the clock during decoding of baseband processor and accuracy of BLF during backscattering period, respectively. The research on the system architecture of baseband processor is conducted, and baseband processor is further partitioned according to the working period of tag. Together with clock management and clock gating, the baseband processor achieves a balanced power distribution during the working periods, and in turn reduces the peak power consumption.2. The research on temperature sensor and the key technique of interface of sensor is conducted. A low-power SAR ADC-based temperature sensor is proposed. The temperature sensor consists of an all-CMOS sub-threshold front-end and a SAR ADC, and the temperature error is reduced by a temperature error compensation scheme. Measurement results show that the temperature error is +0.85℃/-0.69℃ in a temperature range from -40℃ to 100℃, and the power consumption is only 2.02μW. Moreover, in order to reduce the switching energy of DAC during a SAR ADC conversion cycle, two DAC switching schemes are proposed:One is the hybrid switching scheme with the utilization of a third voltage reference Vcm, which achieves a 98.83% reduction in switching energy compared to the conventional scheme; The other is capacitor-splitting switching scheme, which reduces the switching energy by 96.91% compared to the conventional structure, and relaxes the accuracy requirement on the third voltage reference Vcm, resulting in a good trade-off between switching energy and accuracy.3. Based on the above research, two tags are designed by utilizing TSMC 0.18μm CMOS process, one is based on the BLF generation circuit with large clock variation tolerance, and the other is based on the BLF generation circuit with dynamic adjusting technique. The tag based on the BLF generation circuit with large clock variation tolerance has been fabricated in TSMC 0.18μm CMOS process, and various tests have been conducted. Test results show that the BLF generated by the BLF generation circuit with large clock variation tolerance satisfies the requirement of ISO/IEC 18000-6C standard, and the power consumption of baseband processor is 5.6μW. The tag can operate correctly. Under room temperature, the operating range and temperature sensing range of the tag are 8m and 6m, respectively.According to the development requirements of IoT, this paper conducted researches on the key techniques of UHF RFID tag and temperature sensor, and a tag with temperature sensing and identification is realized, which can identify items and monitor the temperature of environment, and further expands the application of tag.
Keywords/Search Tags:UHF RFID, low power, temperature sensor, BLF, DAC switching scheme
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