13.8 A 5.8GHz RF-powered transceiver with a 113μW 32-QAM transmitter employing the IF-based quadrature backscattering technique

Although it is obvious that using a trillion sensor nodes for wireless sensor network (WSN) application would deeply exacerbate the spectral congestion issue, RF-powered sensor nodes [1,2] still support only low spectral-efficiency modulation such as OOK. State-of-the-art standard-compliant RF transceivers for low-power applications have been achieving multilevel modulation such as n/8 D8PSK [3], but their power consumption is as large as 1mW without PA even in the 400MHz band because of the large power consumption of the RF synthesizer, which is required to provide high-frequency accuracy and low phase noise for multilevel modulation. This work presents an IF-based quadrature backscattering technique, enabling n-PSK and n-QAM without an RF PLL. The presented technique exploits the passive RFID technologies, but can realize both amplitude and phase modulation concurrently. Our TX in 65nm Si CMOS achieves spectral efficiency of 3.3b/s/Hz with 32QAM while consuming 113uW with a 0.6V power supply in our measurements, which has 6.6 times better spectral efficiency than previous RF-powered wireless transceivers [1,2]. The prototype RF-powered sensor node with our transceiver including the TX, RX, and an RF energy harvester (RF-EH), succeeds in a wireless temperature-sensing application.