The Design And Implementation Of UHF RFID System

The passive UHF(Ultra High Frequency) RFID technology characterized by high distance, resistance to harsh environments, high accuracy, large memory capacity, and high security features, has been widely used in production, logistics, transportation, security and other fields, and will become one basic technology for information society in the future.The design of UHF RFID chip of our country develops relatively late and the chip market is almost monopolized by foreign companies, To design a UHF RFID chip with own intellectual property rights, based on the protocal of ISO/IEC18000-6C/Gen2, a board-level baseband circuit is designed, associated with RF circuits which is composed of RF chips and an antenna, a reader system with complete function is implemented.As for the digital baseband design, a whole framework of digital baseband circuit of the RFID system is designed. Circuits of Raised Cosine filter and Hilbert filter, the core circuits of the digital baseband transmission link, are designed and implemented, proposing a new design idea of combining the encoding of PIE and the Raised Cosine filter. In the receive link circuits, a high-frequency clock sampling method is proposed for clock synchronization. Through circuit simulation, the Raised Cosine filter and the Hilbert filter in the transmission link work well to produce a single-sideband signal.The receive link circuit samples and decodes correctly when the transmission frequency offsets within the range of +/-22%.To design a hardware platform of reader, A Xilinx Vrirtex-5 XC5VLX110 T FPGA chip with high-performance is choosen to as the core processor of the digital baseband, and a STM32F103VCT6 as the control MCU. The hardwareplatform of the reader designed comprise the FPGA circuit, the MCU control module circuit, the ADC、DAC circuit, the power manage circuit and the RF circuits.In the protocol processing and control section, a detailed analysis of the state hops is made when the reader select, invent or access the tag based on the 6C protocol, and a complete state transition diagram in communication process is established. In accordance with the modular programming ideas, this paper use the model of the finitestate machine, according to the state transition diagram of the protocol, to complete the software design of the control module, which enables the reader to get access to the tag.Through testing, the frequency spectrum of the transmision link of the digital baseband complies with the requirements of the 6C protocol. The digital baseband receiver link can successfully pass the CRC check, and the frame error rate is only 0.05% after the channel filtering, clock synchronization, decoding module and other modules. In testing the entire transceive circuits, the reader can implement a complete inventory cycle by reading the EPC data from a tag, and passing the CRC check, which verifies the feasibility of the baseband functions and the entire architecture of the RFID system.