Biography
Enrollment Date: 2004
Graduation Date：2007
Degree：M.S.
Defense Date：2007.06.09
Advisors：Yongming Li
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Research and Implementation of UHF Low-Voltage Low-Power Passive RFID Transponder
Abstract:
RFID (Radio Frequency Identification) is a kind of contactless automatic identification technology which uses radio waves to exchange data between a reader and a transponder (tag) for the purpose of identifying individual items. Along with the rapid development of integrated circuit design technology, RFID is more and more widely used in various aspects of human life, such as industry automation, supply chain management, transportation control and animal identification. Due to the advantages of long working distance, small size, low cost and long life-time, UHF (Ultra High Frequency) passive RFID tag has become the researching hotspot nowadays domestic and overseas. Since the radiated power of the reader is restricted by different protocols, low-power and low-voltage tag design becomes the key method to improve the working distance of passive RFID systems.
Working principle and energy transmission of passive UHF RFID systems is described firstly. Based on power dissipation analysis of the tag, various low-power design techniques are introduced, including fabricating antennas matching with the input impedance of the tags, designing low-voltage low-power analog front-end and digital circuits, and implementing special low-power rewritable memories.
Low-voltage low-power design techniques of the analog front-end circuits in passive RFID tags are studied particularly. Structure and device selection of the power supply generation circuit is discussed. Dickson voltage multiplier using zero-threshold NMOSFET is analyzed in detail. A large amount of simulation has been made in order to find out how the power conversion efficiency and the output voltage of the Dickson multiplier varies with the transistor size, the capacitance, the number of stages and the load of the supply voltage. Based on the above work, low-power optimization strategies of Dickson voltage multiplier are summarized and a new optimization method is bring forward which accomplishes a higher efficiency by changing the sizes of zero-threshold NMOSFETs used in different stages of the multiplier. Additionally, structures and parameter optimizations of other analog front-end circuits (voltage limiter, demodulator) are discussed in order to obtain the low-power low-voltage properties.
Two kinds of 915MHz passive RFID tag analog front-end circuits based on NCITS_256_1999 are designed, including power supply generation circuit, demodulator, modulator, clock generator, power-on reset circuit and bias circuit. Low-power low-voltage optimization strategies are used during the designing process. The whole tag chips with digital circuits are implemented in 0.18μm CMOS technology. In the end, measurement results are given.