Research On RFID-based Positionable Body Temperature Sensor Chip

With the rapid development of ’Internet of Things’ industry,wearable detection equipment of human body signs as one of the important branches has been widely concerned.The localizable human body signs detection can be achieved through combining the equipment with RFID technology.Thus,RFID(Radio Frequency Identification)is the key technology of positioning function.And the RFID tag whose electric energy comes from the sensing current is usually passive,so the electronic tags can only provide low power.Therefore,this article puts forward a kind of low-power CMOS body temperature sensor which can be combined with RFID tags.The sensor has many advantages,such as small volume and low power consumption,which can be integrated in the passive RFID electronic tags.And the function of temperature detection and real-time positioning can be achieved at the same time.A localizable body temperature sensor chip designed by CMOS process based on RFID technique is proposed in this paper.The chip includes starting circuit,biasing circuit,operational amplifier,core temperature sensor circuit,body temperature voltage output circuit and buffer.The chip whose working voltage is 1.8V and total current is under 40uA can measure the temperature ranges from-40℃ to 125 ℃.The step length of the output voltage is 2.65mV/℃ and the precision of output voltage is 0.01 ℃.The PSRR of output is-82dB.When a 100 kHz frequency sine wave is joined in power supply,the output voltage is stably.The setup time of output is 150us.The body temperature voltage output circuit can amplify the temperature range of output voltage whose step length is 49mV/v between 30 ℃ and 45℃ to improve system resolution.The chip with inner circuit can communicate with RFID tag via a kind of interface circuit.Meanwhile,a localization system based on LANDMARC algorithm is proposed,which can be used for sensor chip positioning.The system test is carried out and the results show that the position error is less than 0.5m within lOmxlOm.and it also can realize real-time transmission and display of the data.