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In this paper, a pair of integrated circuits for general purpose contactless measurement of diverse analog quantities, such as temperature, pressure, humidity, etc., is designed and fabricated in low-cost CMOS process. With one master and one slave chip, the chipset works on the principle of near-field communication (NFC), in which the master chip transmits magnetic energy to power up the slave chip and reads back digitized data via impedance modulation. Compared with traditional NFC-based radio-frequency identification systems, the self-locking operating frequency range is significantly extended from 8 to 12 MHz, providing a robust self-adaptive stability in impedance-varying environments. Apart from an analog port digitized by a built-in 12-bit self-calibrated analog-to-digital converter, up to three switch quantity ports are simultaneously integrated, enabling the chipset to monitor the change of static binary voltages, and provide additional control functions. The fabricated chipset has been successfully characterized and applied to contactless temperature measurement and the switch's on-off detection in a mass-produced household appliance product, showing great potential in various industrial and instrumental applications.
Date of Publication: Feb. 2012