A RF-powered transponder with temperature and photo sensors is designed for environmental monitoring. The transponder gathers its operating power from external ISM (860 - 960MHz) band RF signal and senses ambient temperature and light intensity. The power-efficient and robust clock generator which consists of the temperature compensated ring oscillator and the oversampling synchronizer is proposed. The single slope ADC utilized in the integrated sensors can reduce their power and area overheads efficiently. The internal clock frequency has variation less than 7% for 1.5-V supply voltage and 90℃ temperature changes.
The proposed transponder can operate up to 3.4-m from the base station in the 2-W transmit power and the total power consumption is only 5.1-㎼ during active state. The transponder is fabricated in $0.25-㎛ CMOS process and occupies 0.4-㎟.
