Implementation Of Detecting The Temperature And The Falling Voltage In Passive UHF RFID Chip

A temperature monitor, suitable for UHF RFID is designed, which can be used inenvironment temperature monitor and supply chain. This design applies theTemperature Pulse Convertor mode, which makes the cycles of the signal pulse have alinearity relationship with the temperature. And then we use a base oscillator and acounter to execute the Time to Digital Convertor for the signal pulse. From this method,we can get the cycles of signal from the oscillator under different temperature, and eachvalue of the counter can reflect the current temperature.The design is composed of RF analog part and the digital baseband part.For theimpact of the process and supply voltage variation on the absolute same VCOs can becounteracted in the circuit of RF analog part, the output of the monitor is related withtemperature only. The digital baseband in the design of temperature monitor circuitconsists of a divider of frequency and a counter. The circuit in the digital baseband canproduce a cut off signal for the RF analog part to turn off the oscillator and the basereference circuit, which can reduce the power dissipation.As the time divided module isadopted in this paper, the monitor will be shut down when the temperature is detected.In this module, the problem of recounting can be avoided, and the nomalcommunication between the reader and the tag is not affected.At the same time, the paper has a design for detecting the falling voltage for thenormal write operation to MTP. By detecting the voltage and comparing it with thereferent value, we can assure the next state of the tag and the data reflecting to thereader. And by the method we can make sure that there is enough energy for the writeoperation to MTP.The design is taped out in SMIC0.18μm process. The read and write range of thetag is6m and2.5m respectively inside the room.And outside the room the range of readand write is4.5m and1m, as the data of test shown. And for the temperature monitorcircuit, the counts have a good linearity with the temperature and the temperature erroris less than±2℃during the range of20℃~85℃with a accuracy of0.5℃.The fallingvoltage detecting circuit works very well, which provides a protection for the data inMTP.