Novel Inductive Wireless Power Transfer Uplink Utilizing Rectifier Third-Order Nonlinearity

This paper proposes a new approach for inductive wireless power transfer (IWPT) tag-to-reader communication. A new technique to achieve transmitter/receiver (Tx/Rx) frequency separation is demonstrated. A two-tone Tx is adopted at the reader, and the third-order intermodulation (IM3) frequency generated by the tag rectifier nonlinearity is used as the Rx carrier, which is modulated by a baseband signal sent by the tag. The uplink signal at the IM3 frequency can be picked up by the reader coil. The IWPT impedance matching networks for both the reader and the tag coil can be reused efficiently, since the IM3 frequency at 5.06 GHz is close to the Tx fundamental frequencies at 4.94 and 5 GHz. Due to the Tx/Rx frequency separation, the Tx-to-Rx leakage at the Rx frequency can be suppressed by external filters to improve the Rx signal-to-noise ratio (SNR). The proposed technique is implemented within a 5-GHz IWPT system, and a tiny CMOS tag with a coil size of only 0.01 mm(2) is used. This paper also implements conventional direct and intermediate frequency-based backscattering uplinks for comparison, and the proposed IM3 uplink is able to improve the Rx SNR by more than 20 dB. The achieved uplink data rate (100 kb/s) is also higher than the published work (20 kb/s) that adopted the conventional backscattering method.