A passive long-range UHF transponder with integrated temperature sensor

Recent development in UHF RFID Tags has been focused on the optimization of the powering and communication range of the reader/tag system. The use of low threshold Shottky-diode rectifiers and the rigorous minimization of the tag power consumption have yielded read ranges of more than 10 m for simple identification tags. Sensor transponders that serve as nodes in wireless networks require a more complex chip architecture with a stable, regulated supply voltage and precise current- and voltage references. The analog/digital conversion of sensor data leads to short periods of large current consumption on the tag side. A passive UHF sensor tag was designed in a 0.35 µm CMOS process with Schottky diodes and double poly layers. The tag operates in the 868 MHz ISM band and the air interface is compatible to the ISO 18000-6 standard. The analog front-end with temperature sensor consumes 3.5 µA from the DC supply, which leads to an expected range of more than 3 m. The data rate, the size and the maximum range of each sensor node are significantly improved in comparison with existing LF and HF solutions.