| Radio frequency identification(RFID)is the most representative technology in the Internet of Things and is widely used in warehousing logistics,cargo monitoring,intelligent transportation and other fields.As the coverage of IoT is getting larger and wider,and the application fields are getting wider and wider,UHF RFID with high sensitivity,long-distance communication,multiple information collection,and low power consumption will become an important carrier of the IoT nodes.At long distances,the wireless energy transmission problem and data communication problem of the tag system are two important reasons for limiting its communication distance.For this problem,this paper studies how to improve the RFID communication distance from the system plan and circuit implementation,and has completed the key circuits design of the RF/analog front end of the tag.In terms of system solutions,this paper introduces the bistatic backscattering structure to the traditional RFID system,using independent transmitters and receivers to implement the the traditional reader,separating the uplink and downlink,thereby reducing the energy loss in the uplink and the self-interference phenomenon,the analysis shows that this bistatic RFID communication system has a significant effect on increasing the uplink communication distance,and is more suitable for Internet of Things applications.Aiming at the problem that the traditional RFID reader does not support the bistatic system for large-scale layout,this paper designs a low-power frequency-shifting module to realize the tag reflected carrier frequency band to the NB-IoT system carrier.In order to provide a stable local oscillator clock,this article uses a symmetric load differential delay unit to design a ring oscillation circuit.The output frequency of this circuit is 97MHz,the phase noise is-106.09dBc@1MHz,and the power consumption is 27.6?W.Process fluctuations and temperature fluctuations do not exceed 15%,which meets system requirements.In order to provide bias current and voltage to the system,this paper designs a low-power reference source circuit based on the subthreshold principle,which can provide a high-precision reference current and reference voltage at the same time.In order to reduce the overall power consumption,a super voltage follower structure is used to design LDO to provide a stable low power supply voltage of 1V to the system.In order to realize the local carrier offset,this paper uses a passive double-balanced structure to design the mixer,which is only composed of MOS tubes,the conversion gain is-4.4dB,and the power consumption is 9.9?W.The modulation circuit is also designed to complete the overall circuit design of frequency shifting.In order to achieve a downlink communication distance of 50m,this paper presents a high-sensitivity demodulation scheme.By adding a LNA to the front end of the demodulation circuit to improve the sensitivity of the tag.In order to correctly identify the command from the reader,a high-sensitivity,low-power demodulation circuit based on threshold compensation is designed.The minimum input signal peak value of this circuit is 150mV and the power consumption is 0.672?W.Then an ultra-low power LNA was designed based on current multiplexing technology,with a voltage gain of 30dB and a power consumption of only 0.45mW.The overall simulation results show that the minimum input signal peak value that the tag can recognize is 5mV.Finally,the layout design of the demodulation module is completed,and the tape is tapped based on the TSMC 0.18?m process,and the downlink communication test is performed on the packaged chip. |
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