Biography
Enrollment Date: 2007
Graduation Date：2009
Degree：M.S.
Defense Date：2009.06.09
Advisors：Zhihua Wang
Department：Institute of Microelectronics，Tsinghua University
Title of Dissertation/Thesis：Digital Baseband Circuit Design of RFID System Integrated with Spread Spectrum Technique
Abstract:
The UHF passive Radio Frequency Identification （RFID） technology has been regarded as the most promising RFID technology. The design of reader chip and tag chip plays the most important role in the R&D of UHF RFID, in which digital baseband circuits design is essential in realizing the chip functions and improving the system performances. This thesis completes the hardware design of the digital baseband circuit in UHF RFID reader chip and RFID tag chip, and all kinds of digital signal processing techniques as well as the spread spectrum technique have been applied in the design, improving the performance of RFID reader and the reliability and safety of the RFID communication system. In this paper, firstly, the theories of RFID technique and spread spectrum technique are introduced. Spread spectrum integrated RFID communication protocol is constructed and system simulation is carried out. For hardware circuit design, a processor based on ISO/IEC 18000-6C protocol is designed for the RIFD tag. This chip realizes all the logical functions required by the protocol, and it was implemented using 0.18um CMOS process. Secondly, hardware implementation of digital signal processing for RFID reader transceiver has been realized, including the implementations of digital filterings such as the raised cosine shaped filtering, channel filtering and interpolation/decimation filtering. In order to adapt to the large bandwidth variations without adding more hardware resource, variable bandwidth filtering is achieved in the digital filters design. Both the SSB modulation and DSB modulation are available for signal transmitting. In the case of SSB transmission, the real baseband signal is filtered with a Hilbert filter to create a complex I/Q signal with suppressed negative frequencies. In Reader receiver, parallel correlator is employed to handle the large tag-to-reader link frequency tolerances. Furthermore, spreading spectrum encoding circuit is integrated into the design of RFID tag baseband, therefore the tag could backscatter the response that is spreading spectrum encoded. Correspondingly, spreading spectrum receiver is integrated into the digital baseband of RFID reader, which is used to de-spread the signals from tags. Besides, for the precise synchronization and fine synchronization of PN sequences, acquiring and tracking circuits are devised in the spreading spectrum receiver.Finally, a complete spread spectrum enhanced RFID backscatter communication system is constructed with the combination of the ASIC RFID tag and the FPGA based RFID reader prototype designed above, which is tested under circumstances with different Signal-Noise Ratios (SNRs). Results show that compared with the conventional RFID system which is FM0 encoded in the backscatter link, spread spectrum enhanced RFID system has much better BER performances under noises, interferences, and interceptions.