The design and implementation of an electrostatic discharge protection suitable for UHF RFID devices in CMOS technology is presented. The circuit implements three fundamental functions for the RF interface: power limiting, backscatter modulation and electrostatic discharge protection. Since all functions are achieved by the same MOS device the additional shunt capacitance at the RF inputs is limited. Therefore the maximum reading distance of the RFID device is improved without sacrificing the electrostatic protection level.
Radio-frequency identification by means of passive tags requires low-cost devices featuring extremely low power consumption for long reading distance and compatibility to small printed antennas. The paper describes the design and implementation of the key analog blocks in a RFID chip: power supply regulator, local oscillator and ASK demodulator. The proposed local oscillator exhibits a very low power consumption and achieves a frequency tolerance compatible with the requirements dictated by the ISO 18000-6 standards. In addition, an ultra-low power voltage reference and a regulator based on a zero-voltage threshold device are presented. These circuits are suitable to provide a regulated power supply to the local oscillator and to the core logic of the passive device. Measurements on a chip implemented in 0.18 lm digital CMOS technology validate the results obtained from simulations.
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