An Inductive-Coupling Blocker Rejection Technique for Miniature RFID Tag

Miniaturization is a promising trend for future RF identification (RFID) in many applications such as the Internet of Things (IoT) and implantable devices. For a small-sized RFID tag using near-field communication, the reader is required to emit a large amount of RF power in order to power up the tag while simultaneously picking up a weak backscattering communication signal. This results in a very small signal-to-blocker ratio (SBR), making the demodulation very difficult for the reader-side receiver (RSR). In this paper, we propose a novel blocker rejection technique based on inductive coupling. Several coupling coils and transmission lines are designed and optimized on the same printed circuit board (PCB) with the main power transmitting (Tx) coil of the reader, which leads to a much higher SBR. As a demonstration vehicle, a 200 μm × 200 μm RFID tag with an on-chip antenna is fabricated using 65-nm CMOS technology with a harvested power of 12 μW, an operating frequency of 2 GHz, and a backscattering data rate of 625 kb/s. Measured result shows the proposed block rejection technique improves the SBR by 44 dB.