A wirelessly-powered UWB sensor tag with time-domain sensor interface

This paper presents a wirelessly-powered sensor tag with a time-domain sensor interface for wireless sensing applications. The tag is remotely powered by RF wave. Instead of traditional approaches employing conventional ADCs for quantization and transmitter for data communication, in this work, a Pulse Position Modulator incorporating simple impulse radio UWB (IR-UWB) transmitter is proposed to convert and transmit the analog sensing information in time domain. The analog signal is compared with an adjustable triangular wave for analog to time conversion in signal-varying environments. Then a UWB transmitter converts the PPM signal to very short pulses and sends it back to the reader. The time interval of UWB pulses represents the original input signal in time domain which can be measured on the reader side by a time-to-digital conversion. This approach not only simplifies the ADC design but also relaxes the number of bits transmitted on the tag side. The sensor tag is designed in 180nm CMOS process. Simulation results demonstrate that the proposed approach reduce transmission power consumption by nearly 3 orders of magnitude over traditional approaches, while consuming only 85 µW for 1.5 MS/s sampling rate.