An Analog Front End for a Passive UHF Transponder with Temperature Sensor

We present the analog front-end for a passively powered UHF transponder with integrated temperature sensor that was designed for a 0.35 mum CMOS process with EEPROM, Schottky diodes, and double poly layers. Due to a more complex architecture and additional functionality, the power consumption of the presented sensor transponder tag is significantly larger than that of simple RFID tags. The maximum operating distance is approximately 3 m, which is less than reported values of well over 10 m for state of the art identification tags. The A/D conversion requires a stable, ripple-free supply voltage with a relatively large DC value. The aim of the front-end design in this work is to guarantee the generation and regulation of this voltage, even at a relatively high, time-varying current consumption. The design of the three main circuit blocks (the power generator, the modem, and the clock generator) is focussed on a reliable operation for different temperatures, process variations, and operating distances. All circuits have been optimized to meet these requirements while maintaining relatively low power consumption.