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@mm EEPROM 2P4M process. The core area of the tag (excluding the test bounding pad) is only 756x967@mm^2. The power-optimized tag allows a communication range of more than 6m from a 1W 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 109x47@mm^2 (excluding the counter circuit) and the power consumption of the sensor is less than 600nW. The performance of the sensor is highly linear and the predicted temperature error is merely +/-1.5^oC using one-point calibration within the range of -40 to 85^oC. These properties allow the use of the RFID as a batteryless sensor in a wireless environment temperature monitoring system.