Dual-Mode RFID Tag IC Supporting Gen-2 and Visible RFID Modes Using a Process-Compensating Self-Calibrating Clock Generator

An ultrahigh-frequency (UHF) band passive radio-frequency identification (RFID) tag integrated circuit (IC) supporting both generation-2 (Gen-2) and visible RFID modes is proposed in this paper. Two sources can be used to provide modulated data for the dual-mode tag IC: a radio frequency (RF) or visible light (VL) source. When a modulated RF signal is used, the tag IC operates in electronic product code Gen-2 mode. In the visible RFID mode, modulated VL delivers data and continuous-wave RF provides power for the tag IC. In both modes, power is provided by RF. For the tag IC, a self-calibrating clock generator (CLKG) robust to process variation is proposed. Without a battery, the CLKG has an accuracy of +/- 4% by continuously calibrating its frequency using downlink pulse-interval encoding (PIE) symbols from a reader. In the core of the CLKG, there is a new PIE decoder that reliably distinguishes between data-0 and data-1 under process, voltage, and temperature variations. The tag IC has been fabricated using a 0.18 mu m CMOS process with a chip area of 1.4 x 1.7 mm(2). The power consumption of the tag IC is 64 mu W. Experiments are conducted using a photodiode in the visible RFID mode. With 0.34 mW power from a VL source, the tag IC shows successful detection of VL signal at distances up to 15 m.