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In this paper, we present an improved charge pump circuit for the non-volatile memories in RFID tags. The circuit consists of a single pumping branch without auxiliary capacitors and operates with a simple two-phase clock. The internal high voltages are used to control the gate and bulk terminals of the charge transfer switch. As a result, the threshold voltage loss and the leakage currents are eliminated. An eight-stage charge pump circuit with each pumping capacitance of 0.5pF has been implemented in a 0.18μm standard CMOS process. The measured results show that the output voltage reaches 8.4V with 44MΩ resistive load under the supply voltage of 1.5V and clock frequency of 0.78MHz. The clock driver and the charge pump totally consume a current of 3μA.