A 256-QAM Backscatter Uplink using Delta-Sigma Load Modulation for Ultra-Low-Power WLAN

An energy-efficient and scalable vector backscatter modulator architecture utilizing 1-bit delta-sigma digital-to- digital converter (DDC) based antenna load modulation is proposed. In contrast with the current state of the art (SoA) multiplexer-based M-QAM backscatter modulator that requires M antenna loads, the proposed architecture can be scaled to e.g. 256-QAM using only 4 antenna loads. A 256-QAM, 20Mbps single-sideband, suppressed-carrier backscatter modulator design capable of forming RF channels is developed utilizing 1st order, 1-bit
 DDCs. The proposed design achieves an estimated 60pJ/bit figure of merit which constitutes a 4.4x improvement over the SoA multiplexer-based architecture. An energy model of an IEEE 802.11 compatible IoT device is developed. A battery life of 40 years for an uplink transaction cycle of 1 hour is estimated for an IEEE 802.11 compatible IoT device employing the proposed backscatter transponder. This constitutes a 8x improvement in battery life compared to an IoT device that uses a conventional direct-conversion transmitter.