A 8-µW, 0.3-mm2 RF-powered transponder with temperature sensor for wireless environmental monitoring

We present an RF-powered transponder with temperature sensor for environmental monitoring. The transponder gathers power from the ISM (860-960 MHz) band RF signal. A temperature-compensated ring oscillator and an oversampling synchronizer are proposed for low power and robust system clock generation. The simple structure of the temperature sensor is achieved by sharing major reference signals with the ring oscillator. The generated clock frequency has a variation of less than 5% for 1-V supply voltage and 90/spl deg/C temperature changes. The temperature sensor has a resolution under 1/spl deg/C in the range from -10/spl deg/C to 80/spl deg/C. The transponder dissipates only 8-/spl mu/W during the active state and occupies 0.3 mm/sup 2/ with a 0.25-/spl mu/m CMOS process.