Research And Design Of Receiver Front-end Circuit In The UHF RFID Reader

Radio frequency identification (RFID) technology is a non-contact automatic identification technology which has been used widely. As the size of the RFID tags are becoming smaller and smaller, and the cost of tags are getting lower and lower. RFID will replace the barcode to be used in various fields, such as supply chain management, purchasing, identification and so on. Compared with near field RFID systems, ultra-high frequency RFID (UHF RFID) system has the advantages of a longer communication distance and a higher data rate. Therefore, the UHF RFID technology has become a new development trend of RFID technology.The reader is an important part of UHF RFID systems. Currently, the sensitivity, linearity and integration of many reader receiver radio frequency front-end circuits are not very good, so they need to be further optimized. In this situation, this paper made the reader receiver front-end circuit as the research object, and made a detailed analysis and research on the front-end circuit topology, low-noise amplifier (LNA) and the down-mixer. The main contents of this paper consist of following aspects:(1)A gain controlled wideband LNA is presented in this paper. The proposed LNA combines a cascaded topology with a voltage shunt feedback topology. These two structures make the LNA achieve a good broadband performance. Then the LNA uses a switched gain controlled technology. In the listen mode, the LNA has a high gain. In the talk mode, the LNA has a low gain, which avoid receiver saturation caused by the interfering signals. Simulation results show the LNA exhibits an input matching of-16.97dB, and a noise figure of3.2dB and the third-order input intercept point IIP3of9.26dBm on the frequency band from860MHz to960MHz.(2)A down-mixer with high linearity and low noise figure is presented. This down-mixer is realized through the conventional double-balanced active gilbert-type mixer pair with an improved multiple gated transistor method (MGTR) and a current-reuse bleeding method. The improved MGTR technology allows the mixer to obtain a stable high linearity. The current-reuse bleeding technique is used to reduce the flicker noise of the mixer, and increase the mixer’s conversion gain and LO isolation. Simulation results show the mixer exhibits a conversion gain of19.3dB, and a noise figure of8.02dB and the IIP3of8.86dBm.(3)A fully integrated UHF RFID reader receiver front-end circuit which has a balance performance is presented. The front-end circuit consists of the design of the LNA and down-mixer. The front-end circuit can eliminate the interference of high-power carrier signal, and meet the requirements of the two protocols ISO/IEC18000-6Type B/C. The simulation is made by Cadence Spectre in Chartered0.18μm CMOS process. The results show that the front-end delivers25dB gain with5.29dB noise figure, and the third-order input intercept point (IIP3) of3.37dBm and sensitivity of-97.5dBm in the listen mode. In the talk mode, the gain is19.3dB and NF is9.8dB, the ⅡP3is8.86dBm and the sensitivity is-94dBm. The front-end circuit occupies a chip area of1.5mm2and dissipates14mW from a1.8V supply voltage.