被動式無線射頻辨識系統是目前全世界使用最普遍的辨識系統，在此系統中，被動式射頻標籤藉由讀取器發射出的電磁波獲得能量，並回傳相對應的反向散射訊號至讀取器。然而在傳播路徑衰減的環境下，限制了標籤的讀取距離。多載波射頻辨識系統使用了獨立的連續波發射器來改善此問題，但是在該系統中連續波發射器雖然提供了額外的能量給標籤，卻可能降低標籤接收到的指令訊號之調變深度，而導致標籤解調讀取器訊號錯誤。本論文提出新的被動式射頻標籤解調電路架構，使其能夠在多載波射頻辨識系統裡達到較長的讀取距離。
本論文提出兩種被動式射頻標籤架構，第一種使用被動式電容電感元件組成一窄頻阻抗匹配電路設置於波峰檢測器前端，以避免標籤接收到的連續波訊號通過解調器電路。第二種則使用一帶通SAW濾波器，其設計比照市面上之產品特性，設置於波峰檢測器前端，以濾除標籤接收到的連續波訊號。模擬結果顯示此兩種標籤設計皆能解決調變深度限制的問題，並且與讀取限制之理論分析符合。
此研究使用安捷倫的ADS(Advanced Design System)軟體模擬多載波無線射頻辨識系統，以用來進行本論文提出之被動式射頻標籤設計驗證，並分析其效能及可行性。

Passive RFID system is the most popular system be used all over the world. In this system, a passive RFID tag gains its power from reader emitting electromagnetic wave, and backscatter its responding signal to the reader. However, Because of the large propagation loss, the accessible range of a passive RFID tag is hence limited. In order to mitigate the problems, a multi-carrier UHF passive RFID system utilizes isolated continuous wave emitters to provide additional power to passive RFID tags. This approach however reduces the modulation depth of reader command signals and results in reader signal demodulation error in a passive RFID tag. This work proposes a new passive RFID tag demodulation circuit which can extend the tag read range in a multi-carrier system.
Two types of passive RFID tag architecture are proposed. One uses a narrow band impedance matching circuit before the envelope detector to prevent the signal from the continuous wave emitter passing through the demodulator. The other uses a band-pass SAW filter simulator, which is designed according to the specification of a real product, before the envelope detector to suppress the signal from the continuous wave emitter. Simulation results show that both tag designs can overcome the modulation depth constraint, and are in accordance with theoretical analysis.
This study uses Agilent Advanced Design System software to simulate a multi-carrier passive RFID system, which is used to verify the proposed passive RFID tag design and to analyze its performance and feasibility.

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