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A semi-passive UHF temperature sensor tag compatible with ISO 18000-6C protocol Revision-1 is presented in this paper. Novel power management techniques are proposed to prolong battery life, including two-stage wake-up detection, optimized rectifier design for wireless recharge, quasi CC-CV battery charging, and on-chip battery voltage surveillance. Both real-time temperature sensing and temperature log function are implemented with a bandgap based PTAT circuit. It has a - 40~100°C sensing range with ±1.6°C accuracy. The tag is fabricated in 0.18 μm CMOS technology with EEPROM. Measured sensitivity and standby current are -23.7 dBm and 150 nA respectively.