Research And Design On Radio Frequency Front End Circuit Of 915MHz Reader

Radio Frequency Identification (RFID) has been gradually used in all fields as a new contactless automatic identification technology developed in recent years.Aiming at the weakness of RF analogy front end circuit in ultra high frequency (UHF) RFID reader, such as too many components, high cost, high power consumption, and so on, topology, parameter selection and circuit design are analyzed and studied in detail in this paper. The main contents are as follows:Firstly, the development, working principles and system structure of RFID were introduced, the ISO/IEC 18000-6 type B standard was analysed, and the theory of RF communication system was researched. According to the technical specifications of RFID reader, the paper offers the overall design diagram of the reader and analyzes the structure, working principles and interfaces of the RF analog front end in detail.The RF analogy front end circuit includes transmission circuit and receiver circuit.Secondly, this paper designs the PLL circuit based on digital frequency synthesizer LMX2315, which aims at the requirement and the character of UHF RFID reader. Then it presents pseudorandom frequency hopping program flow chart of PLL. Simulation results show that this PLL circuit has good performance and can be applied to the practical RFID reader circuit. By choosing appropriate IC, this paper designs the RF modulation circuit, RF power amplification circuit and power management circuit which are compatible with the ISO/IEC 18000-6 type B standard. The reader power consumption is reduced effectively, because the reader output power is adjustable and the RF amplifier supply is managed.Thirdly, this paper designs the reflected power detection circuit based on AD8319, and realizes non-load protection by detecting the impedance matching between reader and load continually. Aiming at the requirement and the character of UHF RFID reader, zero-IF circuit has been adopted to reduce the reader cost and power consumption further.Finally, under the system design requirements, a UHF RFID reader prototype was developed. Its hardware was experimented and debugged, and the experimental results and data were given out.The test results show that the prototype's output power, read distance and power consumptio are attained or better than design standards required. The prototype can work stably and achieve the expected goals.