Design Of Front-end Circuit In High Receiving Sensitivity UHF RFID Reader

Radio frequency identification(RFID)technology is an automatic recognition technology that uses the spatial coupling of radio frequency signals to communicate and transfer information with the electronic tags on the target to be identified,and realizes bidirectional non-contact information identification.As one of the key technologies of the Internet of Things,radio frequency identification technology plays an important role in the promotion and development of the Internet of Things.The Ultra High Frequency(UHF)RFID system is a hot spot in recent years.Compared with readers in other working frequency bands,it has the advantages of long distance,rapid identification,and multiple tag identification.This paper designs a front-end circuit of UHF RFID reader with selfadaptive RF self-interference suppression.The main contents of the paper are as follows:1.UHF RFID reader transceiver research: It is mainly divided into transmitter and receiver.The transmitter adopts a direct up-conversion structure which completes the baseband signal modulation,up conversion,filtering and power amplification.The receiver adopts a zero-IF receiver structure,which completes low noise amplification,filtering,and demodulation of the received signal.2.Self-adaptive RF self-interference cancellation circuit research: Due to the use of a combined transceiver structure,strong self-interference signals of the same frequency will be leaked from transmitter to receiver,causing a decrease in signal-to-noise ratio and the isolation of transmitter to receiver,and even causing the LNA gain compression.In response to this phenomenon,an adaptive RF self-interference cancellation circuit is designed to eliminate the self-interference.The cancellation circuit uses a directional coupler to elicit a cancellation signal.The voltage-controlled attenuator and the voltagecontrolled phase shifter are used to realize control of amplitude and phase of the cancellation signal.Finally,the cancellation signal and the self-interference signal are synthesized to achieve self-interference suppression above 40 dB,and the isolation of transmitter to receiver of is over 60 dB.3.Self-adaptive RF self-interference cancellation algorithm: Based on the selfadaptive RF self-interference cancellation circuit,the self-interference cancellation algorithm is studied and designed based on the single-chip microcomputer on the cancellation circuit.The algorithm mainly realizes the self-adaptive control of the amplitude and phase of the elicited cancellation signal.Finally,the cancellation algorithm achieves self-interference suppression above 40 dB,and the convergence time of algorithm is shortened to 32 ms.4.System performance testing: After building a test platform,separate debugging and joint debugging of RF transceivers and adaptive RF self-interference cancellation circuits were done,the relevant performance parameters were tested,and the results were analyzed.