Design Of The Front-end Module For UHF RFID Reader

The electromagnetics theory and communications technology related to the RFID system are discussed in this dissertation satisfying ISO18000-6protocol. With the full understanding of backscatter modulation and variety of modulations, the work principle and composition of the RFID system are described. The design of the front-end module of the reader with long identification distance for the UHF frequency band is proposed. The RF module of the reader is divided into transmitting module and receiving module.In the design of transmitting module, the influence of modulation on the bandwidth of the transmitted signal is analyzed and the use of vestige sideband modulation (single sideband and carrier modulation) is selected, which reduces the bandwidth of the transmitted signal and retains the varied information in amplitude required by the passive tags. In the design of receiving module, the effect of identification blind point is analyzed and the I/Q quadrature demodulation is chosen. The outputs of the I/Q mixers are always orthogonal. The output of I mixer appears zero while the output of Q mixer is the maximum and vice versa. This method solves the zero problem effectively.After deciding the modulation and demodulation methods, the specific structure of the RF module is determined. Transmitting module consists of a frequency synthesizer (local oscillator signal), a quadrature modulator and a power amplifier. Receiving module consists of a quadrature demodulator, low-pass filters, baseband amplifiers, comparators and a Schmitt trigger. Theoretical analysis of the factors affecting the transmitting module and the receiving module such as phase noise, LO leakage and DC offset is presented. Meanwhile, the simulation analysis of transmitting module and receiving module by software Agilent ADS is proposed. Based on the preceding analysis and simulation, the devices are selected to complete the RF module design.