| RFID (Radio Frequency Identification) technology is a technology that incorporates the using of radio frequency signal and electromagnetic coupling to uniquely identify an object. Also, RFID technology uses the electromagnetic coupling to accomplish data transmission between the base station and tags. The advantages of RFID technology are not requiring the transponder to be inline-of-sight, longer distance identification than optical system, readbale and writable tags which can contain large amounts of data, difficult to be counterfeited and higher intelligence etc, which make it to be widespread used in society.In this paper, the basic theory, fundamental operating principles and related stands of RFID system are introduced. Also, the key technologies and solutions of modulation circuits in RFID reader are discussed. In detail, the overall framework of modulation circuits, the basic theory of ASK modulation, characteristics of resonanting antenna, etc are introduced first, and also the limitation routine of the system to the circuit blocks are deduced; And then, the basic circuits of modulation circuits, including Bandgap Reference, CP-Phase Locked Loop and H-Bridge Output are introduced, which are designed exactly followed the system requirements. The details focused on are as follows: the signal flow deduction of Bandgap's Power Supply Rejection Ratio (PSRR), the detection of Bandgap's degenerate bias points and initial accuracy, the design of CP-PLL system model, the phase noise of VCO and the H-Bridge Output's Electro Magnetic Interference (EMI) phenomenon. The simulation results show that circuits design achieves the system requirments.Finally, the modulation circuits'simulation models of RFID system are brought forth, and also simulation results and layout are afforded. The design is implemented with XFAB CMOS 0.6μm process and has already succeeded in silicon verification. The simulation results verify that the design of the circuits fully meets the requirements of RFID system. |
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