Proceedings of the ACM 2nd international workshop on Video surveillance & sensor networks
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A stacked antenna front-end for RFIDs is presented. Schottky diode based voltage doubler charge pumps are used on the front-end. The use of schottky diodes permits broadband operation for UHF (915MHz) as well as Microwave (2.45GHz). The entire chip has a low power EEPROM, digital state machine, clock recovery and data demodulation circuits; and the chip implements the ISO 18000-6B protocol for passive UHF (915MHz) operation. The chip is built on n-well, dual poly digital process with schottky diodes and EEPROM and comparisons are made between an unoptimized front-end built on 1um and an optimized front-end built on a 0.35 process. We provide a theoretical derivation for the superior orientational performance of a stacked antenna transponder as compared to a single antenna transponder. The tag front-end impedance is measured at UHF and Microwave bands for various powers and the threshold power for the tag is calculated. Based on the threshold power measured, the range of the tag is estimated and the omni-directional superiority of a stacked dipole is shown.