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This research describes the design of a fully integrated fractional-N frequency synthesizer for the local oscillator in IMT-2000 system using 0.18-μm CMOS technology and 1.8-V single power supply. The designed fractional-N synthesizer contains following components. Modified charge pump uses active cascode transistors to achieve the high output impedance. A multi-modulus prescaler has modified ECL-like D flip-flop with additional diode-connected transistors for short transient time and high frequency operation. And phase-frequency detector, integrated passive loop filter, LC-tuned VCO having a tuning range from 1.584 to 2.4 GHz at 1.8-V power supply, and higher-order sigma-delta modulator are contained. Finally, designed frequency synthesizer provides 5 MHz channel spacing with -122.6 dBc/Hz at 1 MHz in the WCDMA band and total output power is 28-mW.