Research On Rf Front End Of Passive Uhf RFID Tag Chip

Passive UHF RFID is a typical non-contact automatic recognition technology,which transmits energy and data in space with rf signal as carrier.Compared with other automatic recognition technologies,it has the advantages of low cost,long communication distance,large storage capacity and high security,and its wide application will bring great changes to logistics and commodities industries,so it is of great significance for the research of passive ultra-high frequency RFID.Based on the ISO 18000-6c protocol standard,the radio frequency front end portion of passive ultra high frequency RFID tag is designed with SMIC 0.18 um process.Firstly,the working principle of the passive ultra-high frequency RFID system is introduced.According to the theory of electromagnetic field propagation,the transmission process of RF signal energy between the reader and the label chip is analyzed in detail,and the basic structure of the tag chip is confirmed.Finally completed the design of the RF front-end circuit.The design of the RF front end mainly includes rectification circuit,demodulation circuit and impedance matching of the whole circuit,the operating principle of each module is described in detail during the design process.In the design process of the rectifier circuit,the principle analysis is carried out for the single-stage threshold compensation rectifier circuit.The model of output voltage and power conversion efficiency with the input RF signal amplitude is established and the model is validated,and a three-stages threshold compensation rectifier circuit is designed according to the model.The pull-down current structure is used to replace the low-pass filtering structure in the traditional demodulation circuit to reduce the power consumption and the layout area.The rectifier circuit and demodulation circuit are simulated by Hspice,and the simulation results show that the output voltage of the rectifier circuit is greater than 1.2V under the input power of 45.51uW(-13.4dBm),while the power conversion efficiency of the rectifier circuit is up to 46.77%.The demodulation circuit can work normally with the bias current of 25 nA,and the Maximum error of demodulation circuit is 7.5% in the condition of the protocol.The whole circuit is simulated by ADS.By adjusting the impedance of the antenna,the conjugate matching of the antenna and the tag can be realized.The reflection coefficient is only 0.026.When the antenna is mismatched with the tag,the reflection coefficient is as high as 0.920,and the energy received by the RF front end is greatly changed.The simulation results show that the RF front end works properly,and it is in accordance with the design requirement.