A fully integrated 900-mhz passive RFID transponder front end with novel zero-threshold RF-DC rectifier

This paper presents a fully integrated CMOS analog front end for a passive 900-MHz radio-frequency identification (RFID) transponder. The power supply in this front end is generated from the received RF electromagnetic energy by using an RF-dc voltage rectifier. In order to improve the compatibility with standard CMOS technology, Schottky diodes in conventional RF-dc rectifiers are replaced by diode-connected MOS transistors with zero threshold. Meanwhile, theoretical analyses for the proposed rectifier are provided and verified by both simulation and measurement results. The design considerations of the pulsewidth-modulation (PWM) demodulator and the backscatter modulator in the front end are also discussed for low-power applications. The proposed front end is implemented in a 0.35-[micro]m 2P4M CMOS technology. The whole chip occupies a die area of 490 x 780/[micro][m.sup.2] and consumes only 2.1 [micro]W in reading mode under a self-generated 1.5-V supply voltage. The measurement results show that the proposed rectifier can properly operate with a -14.7-dBm input RF power at a power conversion efficiency of 13.0%. In the proposed RFID applications, this sensitivity corresponds to 10.88-m communication distance at 4-W equivalent isotropically radiated power from a reader base station. Index Terms--Backscatter modulation, charge pump, low power, low voltage, pulsewidth modulation (PWM), radio-frequency identification (RFID), rectifier, RF--dc, zero-threshold.