A 35 pJ/pulse injection-locking based UWB transmitter for wirelessly-powered RFID tags

This paper presents an energy-efficient injection-locking based UWB transmitter for RFID tags in a 0.18 μm CMOS technology. The transmitter is powered by 900 MHz UHF signals radiated by a reader wirelessly, and responds UWB pulses by locking-gating-amplifying the sub-harmonic of the UHF signal. A simple harmonic injection-locking ring oscillator (ILRO) is utilized to generate a 450 MHz carrier for sub-GHz UWB, eliminating power-hungry and complex timing components such as PLL and crystal on tags. The measurement results show that the sensitivity of the ILRO is -15 dBm under 21% locking range without any extra amplifier. Thanks to fast setup time of the ILRO, the proposed transmitter is power-scalable with 35 pJ/pulse energy consumption by duty-cycling. The amplitude of the transmitted UWB pulse is 0.75 Vpp, allowing a pulse rate up to 5 MHz under the FCC regulations. The entire power consumption of the transmitter is 175 μW, which is favorable to wirelessly-powered RFID applications.