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This paper describes a -90dBc@10kHz phase noise fractional-N frequency synthesizer of 110-180MHz output with accurate loop bandwidth control. Stable phase noise is achieved by controlling the bandwidth correctly, even if the PLL uses a noisy but small ring oscillator. Digital controller adjusts VCO gain and time constant of the loop filter. Analog controller compensates temperature variance. Test chip fabricated on 0.13μm CMOS process shows stable and good phase noise performance against process and environmental variations.