Intermodulation Uplink for Far-Field Passive RFID Applications

This work presents the first intermodulation (IM) uplink for far-field power-harvesting RFID applications. The implemented reader sends a two-tone signal for wireless power transfer with a better efficiency, and the tag modulates the rectifier-generated third-order I-M (IM3) frequency for the uplink communication. The IM3 uplink, with different transmitter (Tx) and receiver (Rx) frequencies, allows a direct noise filtering at the power amplifier (PA) output. Therefore, the Rx signal-to-noise ratio (SNR) is immune to the PA output noise. The 5.8-GHz far-field IM3 uplink prototype demonstrates a better Rx SNR and signal-to-blocker ratio (SBR) in the Rx spectrum, compared to the backscatterinz uplink.