A Long-Range UHF-Band Passive RFID Tag IC Based on High- $Q$ Design Approach

We present a fully integrated long-range UHF-band passive radio-frequency-identification tag chip fabricated in 0.35-mum CMOS using titanium (Ti/Al/Ta/Al)-silicon Schottky diodes. The diodes showed low turn-on voltages of 95 and 140 mV for diode currents of 1 and 5 muA, respectively. In addition, the Schottky diodes exhibited low-resistive loss, and a high-Q -factor design approach was exploited to achieve a long read range for the tag integrated circuit (IC). An optimized voltage multiplier resulted in an excellent sensitivity of -14.8 dBm and corresponding power-conversion efficiency of 36.2% for generating an output voltage of 1.5 V at 900 MHz. The range analysis of the measured multiplier performance indicated an operating range of more than 9 m at 4-W Effective Isotropically Radiated Power reader power. The subthreshold-mode operation of an ASK demodulator allowed ultralow power operation. Under power consumption as low as 27 nW, the demodulator supported a data rate of 150 kb/s and a modulation depth of 40%. A new architecture for generating a stable system clock (2.2 MHz) for the tag IC was employed to deal with supply voltage and temperature variations. Measurements showed that the clock generator had an error of 0.91% from the center frequency owing to an 8-b digital calibration scheme.