Design A CMOS Temperature Sensor Integrated In Passive RFID Tag Chip

In recent years, the RFID tag chip integrated sensor is a hotspot of research anddevelopment in the field of RFID, using non-contact manner of RFID technology toobtain the target object temperature, humidity, location and related environmentalparameters, make the combination of sensor technology and RFID technology becomesvery popular and has been widely used.This thesis describes the design of CMOS temperature sensor which integrated on13.56MHz HF passive RFID tag chip. The main considerations on the design of CMOStemperature sensor have two key problems: power and precision. This thesis focuses onresearch the temperature characteristics of bipolar transistor (BJT) in CMOS process,and compare the characteristics of two different parasitic bipolar transistor (lateralparasitic transistor and the longitudinal substrate parasitic transistor) to give the resultlongitudinal substrate parasitic transistor is more suitable to be used to designhigh-precision temperature sensor. The basic principles of chopping technique used inop-amp design, using chopping technique to design a low temperature coefficientbandgap reference, and effectively reduce the op-amp offset and low frequency noise,greatly improve the bandgap reference output signal accuracy, while adding a the VBElinearization to compensate for higher order nonlinear terms. Expound the principle ofuse the parasitic BJT to sense the temperature and circuit design, use chopper op-amp todesign a highly linear PTAT (proportional to absolute temperature) voltage generatingcircuit, and by dynamic element matching techniques to accurately match tributaries ofcurrent ratio, enhance accuracy and linearity of the temperature sensing circuit.Simulating the circuit by adopting Tower0.18um2P6M standard CMOS logicprocess in cadence platform, the results show bandgap reference source from-20°C to100°C temperature range, the output voltage varies only0.35mV and temperaturecoefficient of4.2ppm/°C. The sensitivity of the temperature sensing circuit isapproximately3.1mV/°C, has a very good linearity and temperature performance.