NISP: An NFC to I2C Sensing Platform With Supply Interference Reduction for Flexible RFID Sensor Applications

This paper presents a fully passive 13.56 MHz Radio Frequency Identification (RFID) to I
²
C platform integrated circuit (IC), which has been optimized to reduce supply interference, for RFID sensor applications. In order to reduce the supply interference, this paper proposes a methodology to analyze the power supply rejection (PSR) for the power path. The PSR of the power path is effectively optimized by modifying the low-dropout regulator (LDO) topology. In order to support various highprecision I2C sensors and eliminate the micro-controller, an I
²
C master is integrated on-chip directly. This minimizes the complexity of the overall system. This design utilizes an internal volatile memory to exchange the communication information between RFID and I
²
C. Therefore the RFID and I
²
C communication operate independently, so that both communications can maintain maximum compatibility and flexibility. The chip is fabricated in a standard 0.35-μm CMOS technology and mounted to a tuned RFID transponder coil on an FR4 PCB substrate. Measurements show that the ripple reduction of this proposed LDO reaches 26dB from 400 Hz to 25 MHz in the worst case. During the communication, the ripple of the supply voltage VDDA reaches a maximum 44 mV, while the input ripple of the unregulated DC voltage VDCA reaches maximum 892 mV. A multi-sensor Bosch BME280 is tested with and without supply interference reduction. The result shows that the sensor's resolution improves 6.4 times with the proposed supply interference reduction technique. The RFID to I
²
C platform IC was employed in a demonstrator for wireless real-time measurement of temperature, humidity, and pressure using two commercially available sensor ICs and two RFID readers.