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A 2-V ring-type voltage-controlled oscillator with a 643 MHz center frequency and an 89-% frequency-tuning range is designed with a constant 15-mA current consumption. A prototype achieves a measured phase noise of -108.2 dBc/Hz at 600-KHz offset and a measured differential output amplitude of 1.85 V. Both the phase noise and the output amplitude are relatively constant throughout the frequency range. A 2-V 1.8-GHz fully-integrated CMOS dual-loop frequency synthesizer is also designed with the ring VCO embedded in the low-frequency loop. With an active chip area of 2000/spl times/1000 /spl mu/m/sup 2/, the synthesizer chip consumes 95 mW and has a measured phase noise of -112 dBc/Hz at 600-kHz offset from a 1.87-GHz center frequency.