Research And Design Of Front-end Circuit Module In The Passive UHF RFID Tag Chip

Making use of radio frequency signals, the technology of radio frequencyidentification (RFID) is to automatically capture information in an accurate andflexible way. It is the advantages that make the RFID technology stand out in thefield of automatic identification. With the rapid development of RFID technology inapplication, the tag cost is continually required to fall by making the whole circuitblocks or the whole system integrated into a single chip. Currently, the study anddesign of fully integrated passive UHF radio frequency identification (RFID)transponder has become an important research subject both at home and abroad; itsperformance will impose direct and great effects on the application scope and overallcost of RFID system. In China, the research and application of UHF long rangepassive tags is still in its infancy. Therefore, the study for improving theperformance of the front-end circuit of RF tag crucially has a special significance.In this paper, the constitution of ultra high frequency identification system andits operating principle are firstly discussed in details. Secondly, the systematicarchitecture of passive UHF RFID transponder IC is analyzed and then designed, andthe analysis on the function of cell circuits is also given. Finally, circuits related tothe manufacture of passive tag chips are studied and designed. Specific work andinnovations are as follows:The performance of various types of rectifier circuits which are used in theUHF RFID system is analyzed from the perspective of energy supply. And theNMOS diode charge pump circuit is confirmed as N level voltage doubler rectifier inthe RF front-end of the tag chip. Models are built and theoretically analyzed toprovide a referential basis for improving conversion efficiency. An AC-DC chargepump based on low VTHNMOSFETs is presented, which has successfully eliminatedthe traditional processing defect of incompatibility existing in Schottky diode basedcharge pumps.Various circuit structures of current regulator are analyzed, and anotherprotection circuit for passive UHF RFID tags is proposed for a higher current limit.According to the simulation, when the input voltage has large changes, the outputvoltage has only smaller fluctuation, and the good performance of the circuit istherefore verified with respect to good performance limiting current.In view of the typical low power consumption of passive tags, a voltagereference for analog front-end of tag chip is proposed, the reference which is of full-MOS structure and is based on sub-threshold. It makes use of the positivetemperature characteristic of VTto compensate for the negative temperature of VTHto realize a zero temperature coefficient of output voltage. Aiming for low powerconsumption, most of the MOS transistors in the circuit are operating in thesub-threshold region. Simulation shows that the operating voltage ranges from0.7Vto3.6V and the temperature coefficient of the voltage reference is2.97ppm/℃whenthe temperature is between0℃and120℃. With a1V power supply, the static powerconsumption and the output voltage are1.48μW and430.6mV respectively. Thepower supply rejection ratio is-61dB at1kHz in the absence of any case of filtercapacitor.The layout of the designed circuits is drawn based on the Chartered0.18-μmCMOS technology.