Wirelessly Powered Sensor Transponder for UHF RFID

Abstract

A transponder for UHF RFID with sensor interface for external capacitive sensors is described. The sensor interface consists of a capacitive voltage divider and a 10 bit successive approximation analog to digital converter. The power consumption is about 30 muWDC and the transponder is wirelessly powered with RF waves from the reader device. Wireless measurement of capacitance is demonstrated at a distance of 30 cm with 0.5 W erp transmission power. Low operation distance is mostly due to low efficiency of the rectifying Schottky-diodes in the particular BiCMOS process.