UBC Theses and Dissertations
An efficient CMOS RF power extraction circuit for long-range passive RFID tags Sharif Bakhtiar, Alireza
Effective matching and efficient power conversion play key roles in long- range power telemetry. This thesis discusses challenges and suggests solutions for long-range power telemetry with an emphasis on radio-frequency identification (RFID) applications. As a proof-of-concept a radio-frequency (RF) power harvesting system in a 0.13-µm CMOS technology is designed, fabricated, and successfully tested. The RF power harvesting system must maintain matching over the the wide operation frequency range of passive RFID tags, mandated by EPC- global. In this work, we first analyze the series-inductor matching network and show that there is a trade-o between bandwidth and efficiency. We then derive some guidelines for matching circuit design for RFID tags. To solve the matching problem over a wide frequency range, an adaptive matching system is proposed. At the startup, this system turns on while the rest of the chip is still inactive, and automatically tunes the matching network to achieve its maximum output voltage. Then the rest of the chip wakes up and functions as normal. A new CMOS rectifier stage is also proposed. This stage is capable of efficient operation even with very low input powers. In addition, this rectifier stage can be cascaded to reach higher output voltages without significantly compromising the overall efficiency. Combination of low-power performance and cascadability makes this rectifier suitable for long-range RFID tags. The test setup and measurement results are also discussed in a separate chapter. The measurement results show a 50% rectifiers efficiency at 4-µW input power. To the best of our knowledge, to date, this is the highest efficiency reported for rectifiers operating at such a low input power. Also, as compared to the output voltage at the nominal center frequency of the input matching network, the system shows less than 6% drop in output voltage over the entire 55-MHz bandwidth of the system which verifies the effectiveness of adaptive matching.
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