Full passive UHF RFID Tag with an ultra-low power, small area, high resolution temperature sensor suitable for environment monitoring

An UHF RFID Tag with an ultra-low power, small area, high resolution temperature sensor which adopted double voltage-controlled oscillators (VCO) has been designed and implemented using the SMIC CMOS 0.18 μm EEPROM 2P4M process. The core area of the tag (excluding the test bounding pad) is only 756×967 μm2. The power-optimized tag allows a communication range of more than 6 m from a 1 W effective radiated output power reader.The sensor features independence of process, supply voltage and bias current variation for the double VCO structure. The area of the sensor is only 109×47 μm2 (excluding the counter circuit) and the power consumption of the sensor is less than 600 nW. The performance of the sensor is highly linear and the predicted temperature error is merely ±1.5 °C using one-point calibration within the range of −40 to 85 °C. These properties allow the use of the RFID as a batteryless sensor in a wireless environment temperature monitoring system.