01610851526 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS―I: REGULAR PAPERS, VOL. 53, NO. 3, MARCH 2006 A Spur-Reduction Technique for a 5-GHz Frequency Synthesizer Chun-Yi Kuo, Student Member, IEEE, Jung-Yu Chang, Student Member, IEEE, and Shen-Iuan Liu, Senior Member, IEEE Abstract―A spur-reduction technique is presented to achieve low reference spurs for a 5-GHz frequency synthesizer. A dual-path control scheme incorporated with a pair of the proposed smoothed varactors reduces the gain of voltage-controlled oscillator to less than 15 MHz/V, attenuates the spurious tones, and shortens the simulated settling time by 56%. In, addition, a digital frequency-calibration circuit is used to enlarge the tuning range to overcome process variations. A 5-GHz frequency synthesizer has been fabricated for ve……