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In this paper, we present a low voltage, low power, 2.4-GHz frequency synthesizer designed in 0.35-μm CMOS technology. The frequency synthesizer is implemented with an Integer-N phase-locked loop (PLL). The PLL can achieve a frequency tuning step of 1-MHz and is capable of covering the whole 2.4-GHz ISM band. The voltage controlled oscillator (VCO) output frequency is firstly divided by a novel tri-modulus current-mode prescaler. The prescaler output is converted to rail-to-rail swing and drives the true single phase clocked register (TSPC) CMOS counters. The loop filter is designed to be 2nd order and implemented off-chip with passive devices. The post-layout simulation results show that the phase noise of the VCO is -107 dBc/Hz at 1 MHz offset, and the PLL reference spur level of the PLL is below -50 dBc.