Design Of Passive UHF RFID Tag Front-end With On-chip Antenna

RFID (Radio Frequency Identification) is one automatic identification technology,which utilizes electromagnetic waves or near field coupling to realize non-contactbi-directional communication.Recently,ILT (item-level tagging) has become one hottopic in the field of RFID technology.ILT is able to bring more benefit to customerswho adopt RFID,and it also indicates RFID is applied into more applications.Inorder to meet the strict requirement of ILT upon tag cost and size,this work proposesa set of solutions concentrated on on-chip passive devices,in cornbination with nearfield UHF RFID technology.First,this work utilizes the theory of electrically-small antennas to determine theoperation mechanism and type of UHF on-chip antennas.Then the wireless link ofUHF on-chip antennas is discussed from three perspectives,including magnetic fielddistribution,path gain,and equivalent model.Accordingly,the typical couplingcoefficient between a UHF on-chip antenna and a reader loop antenna is found to beonly 1‰,due to the limited chip size.Lumped models of UHF on-chip antennas areestablished based on the analysis of parasitic losses,and a new model parameterextraction method bearing physical meanings is proposed.Besides,this lumped modelcan cast light on on-chip antenna optimization.This work discussed the feasibility ofusing UHF on-chip antennas to realize the electrical connection between tag chips andoff-chip antennas based on the magnetic coupling.This novel tag package canextinguish the shortcomings of traditional tag package technologies,like relativelyhigh cost and poor reliability.Second,this work discussed the particularity of tag impedance matching,quantitatively analyzed the influence of four common environments upon the tagantenna impedance,including water,metal,glass and dry paper,so as to guide thedesign of the matching zone of tag tunable matching networks.This work proposed anautomatic impedance matching system fit for passive UHF tags,with an emphasis onthe matching zone of on-chip PI-shape matching networks,together with the influenceof the parasitics.Besides,this work studied the feasibility of using the tag rectifieroutput or tag radar cross section to detect the impedance mismatch. Finally,two UHF on-chip antennas and one fully-integrated passive UHF tag chipcompatible with EPC C1G2 protocol were fabricated in SMIC 0.18um CMOS RFprocess.Measurement results are basically in consistent with the theoreticalpredications,therefore verifying the validity of the proposed lumped model and thenear field channel model of UHF on-chip antennas.A reading range in cm scale isdemonstrated to be promising for UHF on-chip antennas.