| Ultra high frequency (UHF) radio frequency identification (RFID) is an advancedauto-identification technology which can remotely identify the targets by employingwireless communication. UHF RFID technology is also an important part of theInternet-of-Things (IOT). Therefore, it has a great prospect and research value. Thisdissertation focuses on the analog and RF front-end of UHF RFID transponders andother relevant circuits, and the main research contributions are as follows:1. Frequency compensation mechanisms for low power oscillator are researched,and an ultra-low-power oscillator with process and temperature compensation isproposed. According to the post-simulation results, the center frequency is1.92MHz, and the power consumption is1.45μW. Considering the temperature(-40~85°C) and process (TT, FF, SS) variation, the maximum frequencyvariation of the proposed oscillator is±5.8%. Compared with other low poweroscillator structures, the proposed oscillator achieves outstanding balancebetween clock accuracy and power consumption. Therefore, this circuit issignificant to RFID transponder chip and other low power systems.2. Design of the average generator in ASK demodulator is researched, and a novelaverage generator based on an adaptively gate-biased MOS transistor isproposed. This design guarantees that the input dynamic range of the ASKdemodulator is large enough, and effectively reduces passive devices in thedemodulator circuit at the same time. Simulations and Measurement resultssystematically validate that the proposed circuit achieves excellent reliability.3. The design and optimization method of dual-output rectifier is analysed. Adual-output Dickson rectifier is implemented and measured. To address theissues exposed in the measurement, a dual-differential rectifier is designed. Thiscircuit structure can effectively avoid the “deadzone” which is observed in themeasurement of Dickson rectifier. The power conversion efficiency reaches72%according to the simulation results.4. Based on the above research results, two tag chips in compliance withISO/IEC18000-6C protocol have been implemented. One of them is based on aDickson rectifier, and has already been fabricated. Measurement results show that the sensitivity of the tag chip is-13dBm, which reaches the performance ofcommercial products. The other one is based on the dual-differential rectifierand the low power oscillator with process and temperature compensation.Simulation results predict that the sensitivity of the tag chip reaches-16dBm.5. Based on the special application requirements in logistics area, this paper alsoproposes the design of a semi-passive UHF RFID tag IC with freight securitymonitoring function. This tag can record the number of times a container hasbeen opened during transport and is compatible with ISO/IEC18000-6C protocol.Several key modules are proposed, such as the switch-state monitoring unit, thepower management unit and the baseband processor. The proposed modules arevalidated by simulations, and the function of RFID transponder is effectivelyextended.6. Low voltage latch-based comparator is a key module in the interface circuitbetween RFID tag and sensor. This paper researches the design techniques oflow voltage latch-based comparators, presents the design of a low voltagerail-to-rail comparator and derives optimal transistor size ratios for bothconventional latch-based and the proposed comparators which operate intransistor sub-threshold region. The proposed optimization method is validatedby simulations and the presented circuit is signicantly faster than existingrail-to-rail comparator designs in ultra-low voltage operation.7. The methods of envelope signal detection in ultra-low power sensor wake-upcircuits are researched, and a novel envelope edge detector is proposed. Theproposed circuit extracts digital bits by detecting the falling edge of the envelopesignal. The proposed circuit needs no fixed bias current, which can significantlyreduce the power consumption of sensor in standby mode. |
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