Research On Key Techniques Of The Front-end For Multi-band RFID Reader

With the proposed concept of the Internet of things, RFID technology has been rapidly developed. RFID technology-based reader is widely used in real life, and the working bands also have covered from LF, HF, UHF to microwave frequency. The diversity of the RFID reader spectrum results in a substantial increase in the processing of data traffic. Therefor, the research and development of multi-band RFID reader has very great practical value.Firstly, this thesis uses PLL frequency synthesizer technology to complete a tunable multiband local oscillator(LO) signal source circuit board and confirms the feasibility of multi-band RFID reader. Secondly, we propose a new multi-band RFID reader transceiver structure based on the design of the tunable multi-band LO signal source circuit board, and the board is completed including hardware and software design. Finally, we establishes a multi-band RFID reader transceiver circuit test platform to carry out the experiment and result analysis.The main contents of this thesis are as follows:(1) Using the PLL frequency synthesizer technology, we propose the tunable multi-band LO signal source circuit structure with the core chip of ADF4351. In the hardware design, we have achieved a 5-way power-tunable output LO signal source circuit boards simultaneously through conducting the loop filter and key signal simulation and high-speed circuit design, and its band covers form 35 MHz to 4.4GHz. Finally, we test and analyze the DDS module output reference signal frequency at 30.72 MHz and tunable multi-band LO signal source circuit board output signal frequency at 433 MHz, 866 MHz, 915 MHz, and 1830 MHz respectively, and all the frequencies were compared with the signal generator. The test results confirm the feasibility of multi-band RFID reader.(2) According to the characteristics of RFID readers, the hardware and software design structure of tunable multi-band LO signal source circuit, we propose a new multi-band RFID reader transceiver circuit structure based on ADL5385 and ADL5380 core chips by using direct upconversion and quadrature downconversion technology. What’s more, we have achieved the transceiver circuit board of tunable frequency band of 433 MHz and 915 MHz by using high-speed circuit design ideas.(3) Design PC interface of multi-band RFID reader transceiver circuit; achieve communication between the PC interface and microcontroller; complete the driver writers of the DDS module, PLL frequency multiplier modules and digital attenuator module.(4) Build a multi-band RFID reader transceiver circuit test platform and complete the signal test of transceiver circuit. The test results show that using the PC interface, multi-band RFID reader transceiver circuit board can work in multi-band at 433 MHz and 915 MHz, and be able to tune span of 30 dB of modulate and demodulate the signal power, achieve the expected targets.