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A 1-V low-power 2.4-GHz fractional-N frequency synthesizer with sigma-delta modulator controller for Bluetooth applications is implemented in 0.18 μm CMOS technology. A novel structure dual-modulus divide-by-128/129 prescaler using a dynamic D-flip-flop is proposed and the operating clock frequency can reach as high as 2.6 GHz at 1-V supply voltage. Moreover, a third-order feedforward sigma-delta modulator (SDM) is employed as a modulus controller to achieve an appropriate division ratio and suppress the fractional spurs. Simulation results show the synthesizer possesses a tuning range of 2.136 to 2.53 GHz and a phase noise of -126.85 dBc/Hz at 1 MHz offset. Moreover, the core area without the SDM and the loop filter is 0.85 mm2, and the total power consumption is 8.94 mW.