| Radio frequency identification (RFID) systems have been developing rapidly in recent years. It has appeared in a variety of fields, such as merchandise circulation, manufacturing, surveillance of people or goods, and so on. The availability of inexpensive CMOS technologies that perform well at microwave frequencies has created new opportunities for automated material handling within supply chain management that will, in hindsight, be viewed as a revolutionary technique.This paper focuses mainly on UHF passive RFID tag and presents basic principles and design methods of several key circuits of the tag. The author begins from the analysis of the basic structure and principle of the UHF RFID tag. After the analog front-end circuit structure being researched, the central work of the paper is present, which is the design of modem system and power-on-reset circuit (POR) and current reference circuit of the tag. About modem system, this paper first presents some basic theories, like sorts, physical principles, realizing methods and air interface requires, and then, presents the circuit structure. About the POR and the current reference circuit, the author gives us some new improvement on conventional circuit. After the circuit design, the paper presents the layout of the above circuits and the overall layout of analog front-end circuit. All the circuit and layout design are on the basis of SMIC 0.18μm CMOS technology.The paper makes efforts on the optimization of the circuit structure and performance and power consumption. POR circuit has achieved zero static power consumption. In the current reference design, subthreshold technique is used, and the reference current achieves only 100nA. Modem system uses ASK structure to be compatible for different air interface protocols. In the modulator design, modification on conventional circuit structure is introduced, which made this module be more compatible for a large input voltage range and different modulation depth. |
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