Abstract: A low voltage high efficiency charge pump circuit for passive UHF RFID is presented to increase the operating range of tags. The bias voltage supplied to the main charge pump by the bias circuit is raised by suppressing its load current using a diode connected MOSFET, which greatly reduces the threshold voltage drop in traditional charge pumps, suppresses the reverse leakage current and improves the sensitivity and power conversion efficiency. The charge pump has been fabricated in chartered 0.35 μm CMOS process. Measurement results show that a 275 mV minimum input level is required to generate 1.47 V power supply for 200 kΩ load and efficiency up to 26.2% is achieved. The maximum operating range of the RFID tag with this charge pump is 4.2 m. This design effectively contributes to the good performance of RFID chips.