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1. PASSIVE AND SEMI-PASSIVE WIRELESS TEMPERATURE AND
HUMIDITY SENSORS BASED ON EPC GENERATION-2 UHF
PROTOCOL
ABSTRACT
This paper proposes passive and semi-passive wireless temperature and humidity sensors
based on electronic product code (EPC) global Class-1 Generation-2 UHF communication
protocol. The wireless sensors consist of a sensor key chip and off-chip temperature and
humidity sensors. The sensor key chip integrates RF/analog front-end circuit, digital baseband
processor, nonvolatile memory, on-chip temperature sensor, and sensor interface. The sensor
interface connects the off-chip sensors and the sensor key chip. The sensor key chip with the on-
chip temperature sensor can operate without battery power (passive mode), and also can co-
operate with the off-chip temperature and humidity sensors powered by battery (semi-passive
mode). The RF/analog front-end circuit provides the dc power to the sensor key chip and
communicates with the interrogator passively. Advanced low-power techniques are adopted to
reduce the power consumption of the sensor key chip. The sensor key chip is fabricated in 0.18-
μm CMOS process. In passive mode, the maximum wireless sensitivity of on-chip sensor is -
15.1/-11.2 dBm for reading and sensing operation, respectively, and the temperature sensing
error is -1 °C/0.8 °C over operating range from -20 °C to 50 °C. It achieves a reading/sensing
distance of over 9.5/6 m with 4-W effective isotropic radiated power (EIRP) by the commercial
interrogator. In semi-passive mode, the temperature and humidity sensing distance of off-chip
sensors is 2.7 m.